


A Study in Human Biology

by NoelleLilacNotte, Yiiiiikes



Series: An Alien, a Xenophile, and Her Brother Walk Into a Bed [1]
Category: Invader Zim
Genre: Accidental Voyeurism, Birth, Biting, Breeding Kink, Consensual Incest, Dehumanization, Dom/sub, EGG Birth, Egg Laying, Eggnancy, Everyone is a dumbass, Heat Cycles, Incest, Knotting, Love Triangles, Marking, Multi, Oviposition, Possessive Behavior, Possessive Sex, Pregeggnancy, Science Kink, Sexual Punishment, Sibling Incest, Species swap au, Stalking, Threesomes, Twincest (implied), VERY inaccurate birth, Voyeurism, abnormal cum, egg pregnancy, everyone is moronsexual, excessive cum, inaccurate birth, its kinda mild tho, kink fodder, mild dubcon, tentacle cock, that end in polyamory, xenophillia
Language: English
Status: In-Progress
Published: 2020-02-24
Updated: 2020-04-24
Packaged: 2021-02-19 10:48:28
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 10
Words: 26,970
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22876423
Author URL: https://archiveofourown.org/users/NoelleLilacNotte/pseuds/NoelleLilacNotte, https://archiveofourown.org/users/Yiiiiikes/pseuds/Yiiiiikes
Summary: A perfectly normal scientific research mission on an alien planet goes awry, in the best way possible.
Relationships: Dib/Reader, ZaDr/Reader, Zim/Reader
Series: An Alien, a Xenophile, and Her Brother Walk Into a Bed [1]
Series URL: https://archiveofourown.org/series/1647340
Comments: 19
Kudos: 116





	1. Log Date: 413612777

**Summary for the Chapter:**

> Finding interesting subjects on a new planet is easier than expected.

**Notes for the Chapter:**

> Irken Dib is a sciencey dumbass who thinks aliens are hot, prove me wrong.

**LOG DATE: [413612777 at 11:46pm Local Time]**

_The denizens of the planet Urth seem relatively stupid. While they have the technological capabilities of a Class C civilization, I have found that their individual intelligence is lacking, much more reminiscent of a Class G civilization. There are outliers, as always, but none so far that seem to care about hindering my work._

_I have blended in with the local fauna flawlessly. They dispense information, however primitive, when questioned. So far the only potentially useful leads are their snack-making machinery and a strange method of reproduction that only requires two humans, no control brain processing needed._

_I was given was is apparently called a “death glare” by a block-mate today. According to data records, his name is Zim. He appears to be one of the more intelligent members of this primate society. He has what is called a “sister”, who appears to be similarly high on the intellectual ranking chart. This “sister” seems to be a glorified assistant, perhaps the human equivalent of a SIR Unit. Not all humans seem to have a “sister” of their own, possibly they are exclusively for higher ranking members of the hierarchy._

_The pair of them are very rarely apart. The Zim human seems particularly attached to his “sister”. Cursory scans suggests genetic compatibility, they could be excellent subjects for a study on this species’ reproductive biology. It is an interesting concept, however primitive and unpleasant._

_Signing off, Invader Dib._

**MEMO CLOSED.**

It had only been 3 klicks on the barren ball of dirt and organic filth locals had called “Urth” before Dib ran into a metaphorical roadblock. It had also taken him 3 klicks to learn that when a human says something, they do not always mean it to be true, and that was called a “metaphor”.

Human’s existence, and subsequently every aspect of their society, was a foreign and unnecessarily complex fluke of nature. Everything worked, and the majority of the ~~Urth~~ Earth (his mistake. Dib made a note to fix his earlier memo) people seemed to know the intricacies of their society in depth, but none of them could explain it when asked.

The metaphors, and all of human culture, confused Dib, and he was not the sort of soldier to just accept the unknown. Dib was an _Invader_ , and had scientific training on top of that. It was Dib’s job, no, his _purpose_ to discover the fantastical and bring it to light.

And if that meant siting in an uncomfortable chair, in an uncomfortable disguise, receiving uncomfortable glares from one particular school-goer, then so be it.

Dib wasn't sure what exactly he'd done to invoke Zim's hateful gaze but if he had to venture a guess it was probably some arbitrary human social custom that he had neglected to perform. And if he had to venture a more detailed guess it was probably something to do with the girl that Zim referred to as 'Sister.'

She went by other, less important names but more often than not she was just called Sister. At least, by Zim anyways.

Sister had been one of the more clever humans, and she was quick to explain herself when Dib asked her to. But just like Zim, Sister gave him strange looks too.

Although, these ones were much harder to understand.

When Dib saw Zim's expression he recognized it immediately as annoyance, anger even. It was not an unfamiliar expression to the Irken. The looks Sister gave him were more complex.

Like Zim, Sister was not quick to break eye contact, a clear indication that she would not back down from a challenge. Dib respected that. However her stare didn't hold the same heat as Zim's did. The closest thing Dib could get to identifying it was curiosity. But even that felt inaccurate at best.

Sister had exchanged a few extended conversations with Dib on the rare occasion that Mr Sizz Lorr (who was of the rank “Teacher” and apparently respected and feared by his underlings) was distracted or disinterested enough to allow for such an exchange.

During their first interaction, Sister had given an “apple” to Dib, and introduced herself and her ~~master~~ brother (title implications unknown), Zim. Apparently it was human custom to give new members of your microcommunity an offering of food in hope that they do not choose to destroy you.

The Apple was sent to Dib’s base lab for testing.

Zim was not nearly as submissive as to give Dib offerings. He seemed offended in fact, that Sister chose to interact with Dib at all. With an annoyed flourish and an arm over the smaller creature’s shoulders, he had even physically pulled her away.

This Zim was sure to be a worthy opponent, if his unwillingness to submit to a new entity of unknown power was anything to go off of. But he seemed very attached to his underling. Dib made a note to explore potential ways to exploit this weakness.

In that moment, the planet Earth began to shape into a much more interesting conquest.

With a little bit of ~~stalking~~ field research, Dib figured out that Sister had what was referred to as a 'free period' in the hour block before food was served. This Free Period was the only time of day when Zim wasn't vigilantly monitoring her.

And it hardly took him a minute to change his Class Schedule so that he too had a Free Period.

It didn't take him long to locate Sister during the Free Period. She was in the Library, a primitive human information center, and also the place where all of the Free Period children had to go. Since Sister had been open and ready to divulge information at first contact, Dib assumed it wouldn't be too hard to extract something valuable from her when he spoke to her again.

He was wrong.

When pressed for information again, Sister simply repeated that The Library was a silent place. Dib idly wondered if such silence was meant to be a punishment, as humans seemed to enjoy day-to-day stimulus, or if the break from such input was a form of reprieve.

Sister did, however, inform Dib that the processed tree corpses that The Library was full of were called “books” and they they contained information. The ability to “read” was required to understand the primitive printed words, but Dib’s pak was able to copy and absorb the necessary information from an unsuspecting bystander. It seemed that the Library and its books were yet another form of entertainment stimulus.

“How fascinating.” Thought Dib. “The humans spend so much time making up new forms of time-wasting. How do they get anything done?”

Dib set out to fill his pak’s data storage with as much information as he could from books alone. This proved to be a somewhat fruitless endeavor, as the vast majority of the books in The Library were something called “fiction”, in which the writer lies to the audience for the audience’s amusement.

Unfortunately, that meant Dib’s best lead was still Zim and Sister.

For the next several day cycles, Dib would spend Free Period in the Library, attempting to coax Sister into divulging more information. It seemed to be a fruitless cause, however she did greet him in the halls more often now, so perhaps that was a small victory in its own right.

After a while however, he decided to abandon the plan of seeking out information in the Library. If he wanted to understand humans, he was going to have to do some more field research.

Which is how he ended up in the Boys Bathroom listening to Zim make the most _peculiar_ noises.

A strange mix of growling and a noise that sounded like pain. At first, Dib was under the impression that Zim had found himself in a scuffle, perhaps he’d encroached on another human’s territory or food supply. He was very incorrect.

Instead, Dib found his adversary in what he could only assume was a compromising position. Zim’s normally immaculate overlayer (called a hoodie by Sister on one occasion) had been draped over the flimsy stall door. The uncomfortable-looking rough black material of his pants, along with some much softer-looking purple secret pants, had been shoved down to Zim’s knee joint.

He had his hand wrapped around a part of his anatomy that Dib had never seen before.

And he was talking.

“Stupid new kid, acting like he has any right to come onto _my_ sister? He has no _idea_ who he’s messing with. I’m going to _destroy_ him, and make sure he knows exactly who she belongs to.”

This was an interesting development. Dib wondered what purpose this action served. He was tempted to just ask Zim but when he took into account the abnormal situation he decided that it would probably just be safest to observe for now.

He made a mental note to do further research into the name Sister and what it meant. He'd heard other kids say it but when asked they would deny that they were referring to Sister. Every time they would respond with something like, "no not her, _my_ sister!"

Oh! How could he have been so foolish? Sister wasn't a name it was a rank! What exactly that rank entailed was still beyond his knowledge, but regardless of that Zim seemed to be very possessive of his Sister.

So much so that he looked at pictures of her with significantly less clothing while he stroked his appendage.

Dib decided to take things to Sister directly, as she’d at least been _somewhat_ receptive to his questioning. She had even given him a thing called a “compliment” which appeared to simply be meaningless praise from someone who’s rank was equal or lower to yours.

She was correct in her assessment of his disguise’s coat. It was _very_ cool.

Cool, Dib reminded himself, in that it was a testament to his status, akin to a trophy. Not cool as is in having a low temperature. Dib _refused_ to make that mistake twice.

“Hello, Zim’s Sister!”

“I have a name, but go on.”

“I have a proposition for you. I require answers to some rather pressing questions, and would prefer to do so away from Zim, or any other life forms for that matter. I am prepared to offer foodstuffs and entertainment of your choosing in exchange for these answers.”

“Are...are you asking me to hang out with you?”

“Is that the term?”

“For what you just described, yeah.”

“Then yes.”

“Uh...sure. I’ll bring some books over, the library doesn’t always have the good stuff.”

“Good stuff?”

“Yeah, y’know. Banned books. Lolita, Flowers In The Attic, Twilight. Ok maybe Twilight kinda sucks but still, way more interesting than Generic White Guy is Special.”

“Ah, I knew the Library was hiding things!”

“Yeah, schools do that. Anyway, how about Friday? I’ll just walk home with you.”

“Acceptable! We shall reconvene at the appropriate time!”

As Sister walked away, Dib could only wonder about how much information he could gather from her _without_ her pesky Brother around.

Earth was shaping up to be _very_ interesting indeed.

_Dear Stupid Fucking Diary,_

03/17

The new kid has been making a point to antagonize me. I don’t know WHY he does it or HOW he intends to succeed should I choose to engage with him, but it’s getting REALLY ANNOYING. He’s been staring at me like a creep during class, and now he’s even hitting on my sister! It’s INFURIATING that she can’t see through his OBVIOUS LIES.

He seems incapable of understanding the concept of PROPERTY. Of CLAIM. If he intends to steal her away from me, he should CHALLENGE ME DIRECTLY instead of being a COWARD and talking her up in the library where I CANT fight him.

Unfortunately, she seems to still be INSISTENT on being his friend or whatever, despite my MANY protests and the fact that she has ME, ZIM, to keep her company.

It’s becoming increasingly more frustrating, and Gir, that goddamn dog, has been stealing my leftovers from the fridge. I still do not know where he learned to open the door.

_Fuck you, Diary. Love, Zim!_

**Notes for the Chapter:**

> I hope I captured Zim’s crackhead energy sufficiently in that diary entry.


	2. Call Me Master

**Summary for the Chapter:**

> The new kid’s a lot stupider than you originally thought.

**Notes for the Chapter:**

> Did we go overboard with this chapter? Absolutely. Did we enjoy every second of it anyway? Of course.

The Hanging Out, as Sister had called it, was somewhat enlightening to Dib. It certainly wasn't the most efficient way of gathering data but there was something oddly thrilling about being alone with her.

Sister had insisted on taking Dib to a "super cute hole in the wall coffee place, that you're gonna fucking love!" Dib didn't protest at all, mostly just curious about what why she would be taking him to a hole in a wall.

They spent most of the Hanging Out sitting together in squishy chairs while Sister explained books and the concepts of human taboos to him.

"I'm sorry, are you actually saying you have no idea what incest is? Or pedophilia? Do you at least know what sex is?"

Dib wanted to bluff his way through the conversation so that Sister wouldn't get suspicious, but what he wanted more than that was answers.

“I...didn’t get taught.”

“Yeah but didn’t you go to school? Didn’t you at least get curious and make use of the internet? Or are you like, from one of those Amish families that doesn’t let you have technology?”

“Yes, that. I am from Amish.”

“...sure dude. Look, I probably shouldn’t be the one explaining this to you, but clearly your parents haven’t done the job. I know the feeling, I had to get all my info secondhand from Zim, or from our cousins.”

“Cuz-in?”

“Uh, my aunt, my mom’s sister’s kids. Red and Purple, stupid names I know. Aunt Miyuki is kind of weird like that. They’re older than me and Zim though, so we learn from them sometimes if Zim bugs them enough.”

“This explains a few things.”

“Wait, really? Like what?”

“I apologize in advance if this breaks some form of social contract, but I have observed you and your...Brother, and the other humans do not seem to engage with you as much as with each other.”

“Oh, that. Yeah, Zim’s not exactly easy to get along with for a lot of people, especially when he gets jealous.”

“Gelatinous?”

“No, jealous. Like, when he thinks someone is trying to take something important to him, he gets defensive and lashes out at them.”

“Ah, territorial.”

“That’s one way to put it.”

"So I can assume that Zim is your superior then?"

"What the fuck?! No the hell he is not, and don't let him hear you say that! He's got a big enough ego as it is!" Sister was less than pleased with Dib's assumption but he couldn't for the life of him figure out why!

"So, you're his superior? Or are you of equal rank?" He was getting a bit bold with the questions now but Sister seemed much more passionate in her reaponses now than she had before.

"Neither of us is superior you weirdo, God! Now do you want me to give you your abridged sex ed class or not?"

"Yes, do please get on with the lesson." Dib said. Sister opened her mouth to speak but seemed to struggle at making the words come out. Dib almost thought she was suffering some type of illness until she finally managed to choke out a few simple sentences.

"Fuck, I'm not qualified to explain this to somebody! Just google sex, God!" She whisper shouted and covered her face with her hands.

"What about those other two things?" Dib asked, making a note to find out what a google was. Sister screamed into her hands for a moment before uncovering her mouth to speak to him.

"Incest is when relatives have sex and pedophilia is when an adult has sex with a child now can we please just talk about books again?"

Dib sighed in annoyance at her unsatisfactory answer.

"I think I've gathered enough information from this Hanging Out." He said and stood up to leave. As he was gathering his things, he heard Sister's primitive communication device play a loud, tinny sound before she picked it up and held it to her face.

"Hey Zim I'm- oh my God, no I didn't get kidnapped! I'm just out! I don't have to tell you who I'm with all the time!" Sister's face turned a bright shade of red and her eyes widened. Dib really wished he had brought tools to allow him to hear Zim's end of the conversation.

"Yes, I'm... I'm out with Dib. God will you stop freaking out? I'm already on my way home!" Without even giving Dib a farewell, she had left the building.

How strange. Perhaps he would be better off just observing the two as opposed to actively seeking information from them.

Observation was one thing, but Dib couldn’t get proper readings of their brains, neurochemical releases, there were just too many variables to account for in the wild. Dib didn’t have a controlled environment to—

Oh.

_Oh!_

Of course, how could he forget! He had a holo-simulation room for just these sorts of studies! After all, being able to eliminate unnecessary variables was a key part of collecting accurate data. It wouldn’t even be difficult, just a minor memory transplant, and setting the room to display a room from the subject’s dwelling.

Zim’s room, and a short walk home should suffice.

Dib set his computer to record, sat back in his observation chair, and let the scene play out in front of him, taking note of the rises in adrenaline, oxytocin, dopamine, testosterone, and various other chemicals in both parties systems.

He was also quite intrigued by their verbal interactions.

“Zim, c’mon, it’s not that big a deal, it’s not like I was screwing the guy.”

“ _You_ may not have wanted that, but that... _obnoxious asshole_ did! My perfect eyes could spot his plans from a mile away!”

“Ok, first off I know you wear contact lenses, second, what are you getting so worked up about? He’s just being friendly. I swear, he doesn’t even know what sex is.”

Hah, little did she know, Dib was bound to find out sooner or later! Zim’s angry growling didn’t stop the whole way home, and neither did Sister’s little sighs. She didn’t seem angry, as she should have been if he was an underling, or scared, as she should have been if he was the superior.

The best way Dib could describe her was “affectionately annoyed”.

Or at least she was, until Zim pushed her onto his sleeping apparatus (a bed, according to a couple of books) and _snarled_ at her. An aggressive smirk, a dark chuckle, and Zim had her pinned to the thing.

“Good girl.”

Now _that_ did something.

Dib could practically see the hierarchy fall into place. Sister’s posture was instantly relaxed, expectant, _submissive_. Zim’s growls and laughter mixed into one continuous noise, and even if he didn’t have his hands on either side of Sister’s head, with her thighs spread apart with his own, he was very clearly in control.

And Sister was very clearly enjoying it.

"Zim, I told you nothing happened!" Sister insisted, although her voice was fair more airy than when she last spoke.

"That's not the point and you know it." He growled, and sister whined, seemingly unknowingly spreading her legs further. Was that some kind of human gesture of submission? Dib took note of her actions.

"You can't just go out with some stupid jerk and not expect punishment."

"Zim, I-" Zim cut her off by pressing his mouth against hers. It seemed like some sort of battle, one that Zim was clearly winning. Sister whined and opened her mouth to let Zim's tongue dart in.

Dib was startled by the unfamiliar feeling he was getting from watching these humans fight.

Sister seemed to relax as Zim took control of the situation. Even when he sat back up, leaving her at an awkward laying-down angle with her hips elevated, she simply fell back into the (admittedly, very comfortable-looking) blankets.

Zim shucked his hoodie down his shoulders, then tossed it unceremoniously to a random corner of the room. This made Sister turn a different color, a warm reddish.

Zim’s hands ran down from their position cupping Sister’s face, trailing down her neck, chest, sides, before he grabbed roughly at the hem of her shirt and pulled it over her head, throwing it off to join the other she garment.

Apparently, both Sister and Zim wore another garment under their outer layers. Zim’s being a basic black thing (a tank top, if Dib recalled correctly), and Sister’s being...well, smaller, and much more shapely. Zim seemed _particularly_ pleased to see that.

He licked the skin around the edges of her garment, making her shudder.

"Please, more Zim I-" Zim cut her off by delivering a sharp slap to her ass, surprising Dib. He understood that this was some sort of fight but up until now it had seemed more playful than violent.

"That's not my fucking name." Zim growled, and squeezed the clothed flesh that he had just assaulted. That statement confused Dib. Why did everyone call him Zim of it wasn't his name? Was this similar to how only Zim called her Sister, or was this some sort of bizarre situational naming system that he didn't yet understand? His questions were not answered in the slightest when Sister responded.

"I'm sorry sir!"

“Good girl.”

Sister shuddered at that, letting her arms fall limply beside her head, and closing her eyes as Zim continued licking and biting at her body.

There was that statement again, just a simple phrase. Could Zim’s status be so above hers that even minor praise was enough to satiate the desire for recognition? Or was it something more, a code, a cipher, or some form of bastardized language Dib wasn’t privy to? So many questions, so many theories.

“Now, what are we doing here?”

“I’m...I’m being punished, Sir.”

“And what are you being punished for?”

“For being disobedient?”

“Wrong.” The statement was punctuated by another sharp slap on her rear.

“I’m sorry Sir, I don’t know!”

“You are being _punished_...” Zim growled. “For letting some _weak little loser_ touch what belongs to _me_.”

Well this was making less and less sense to Dib by the second. He had been wrong about this being some sort of fight, according to what Zim said it was a punishment. But how could it be a punishment if Sister seemed to be enjoying it so much?

"I'm sorry sir." She said quietly, and Zim leaned down to press his mouth against hers again. Their movements were slower this time but they were no less sloppy than they had been the first time.

"I don't think just spankings are going to he enough punishment this time." Zim said. Sister had a hard time keeping her breathing steady. "What do you think would be an appropriate punishment for you today?" Zim inquired.

"I don't know sir." Sister replied. Zim squeezed the meat of her ass that he had previously hit, making her whine and squirm.

"I think I have an idea." Zim said. His tone was threatening but still, Sister made no attempt to escape or fight back.

Zim took his thumb and traced it over Sister’s bottom lip, using his pointer finger to tilt her chin slightly upwards. His other hand fumbled with the button on her jeans, popping it open without ever breaking eye contact.

When Sister finally blinked and broke the spell, Zim pulled back and removed his shirt, leaving his entire top half exposed, and letting the rumpled waistband of his purple under-shorts ride up past the hem of his jeans. Sister followed suit, bringing her hands behind her back and yanking her top off.

Upon closer inspection, Zim seemed to have bits of metal stuck through the pair of dots on his chest. Dib wondered idly if they hurt.

One of Zim’s hands came up to Sister’s chest, squishing one of the malleable mounds of flesh. His other hand came up to her wrist, pinning it to the bed beside her.

“You’ve had that pretty little neck on display all week, haven’t you, _pet_? I’d say it’s only fair to mark it up if you’re going to make me take such measures to ensure I’ve staked my claim properly.”

"Yes sir!" Sister said.

"Good girl." Zim replied. Then he bent down to bite and suck on the flesh of her neck. The noises that she made in response were difficult to distinguish. Was she in pain or was she enjoying the experience? And why did Dib feel so uncomfortably warm?

Zim slipped his hand down Sister's pants, doing something to make her mewl and whine. He pulled his mouth off of her neck to reveal a deep purple spot forming on her skin. He licked it quickly, then tilted his head to leave another mark.

Dib could sort of make sense of that. The marking must have simply been a territorial thing. That didn't exactly explain why Zim made Sister say "thank you, sir" after he left each mark.

Sister’s words were slowly becoming more and more incoherent. Her breathing was shaking, and it was clearly interfering with her ability to speak. For some reason, the increased difficulty in communicating seemed to please Zim.

“Are you enjoying yourself, little whore?”

“Y-yes, Sir!”

“Well too bad. You don’t get to cum until I do.”

Zim’s hand returned to Sister’s now-busted lip, brushing over the tiny red cut with his thumb before he leaned down to lick the small bead of blood that he formed on it.

“Do you think you can handle that? Can you hold yourself back until I _say_ you can cum?”

“I’ll try, sir!”

“Don’t try, succeed. Now shut up and lie back, be a good little girl and relax.”

With that, Zim yanked her pants down around her knees, then roughly tugged them off, one leg at a time. She didn't wear any additional garments like Zim's under shorts, which appear to simultaneously delight and enrage Zim.

"You didn't even wear panties today, you filthy little slut!" He exclaimed, spreading the folds between her legs with his fingers.

"I-I'm sorry, sir?" Sister said tentatively, unsure of whether or not she would be punished for her careless actions.

"You're about to be sorry." Zim said, then scooted back to place his face between Sister's legs, licking and sucking on her similar to what he had been doing to her neck.

She whined and squealed and when she buried her hands in Zim's hair, he bit her. The bite made her scream and kick, but Zim held her down as he nibbled on her sensitive flesh.

Sister’s hands flew to her mouth, clamping over it in an attempt to keep the little screams and moans in. Zim seemed doubly determined to get her to make those noises, quickening his pace and gripping at Sister’s thighs.

One of Zim’s hands left Sister’s leg, snaking into his pants and tugging them down. He pulled out the same member he’d been holding in the bathroom, and made the same rapid jerking movements he’d done then too.

This seemed to make Sister a bit more confident, or perhaps just troublesome. Either way, the way she leaned up on her elbows and punctuated her words seemed somehow disobedient.

“Impatient, Sir?”

Zim did _not_ like that. He pulled his face off of Sister with a growl, moving his hands to her shoulders and shoving her back down. The thing Zim had been stroking was shoved up against where his tongue had been, and it made Sister squeal.

"Do not talk out of turn, whore!" Zim growled. He was grinding his hips against Sister frantically, both of them struggling to breathe and growing more and more sweaty.

"I'm sorry sir!" Sister whined, tears welling up in her eyes. When one of them fell, Zim leaned up to lick it off of her cheek. "Please sir, I need to cum! I can't hold it in this time, sir please!" She begged.

"I already told you, you don't get to cum until I do!" Zim insisted, still rutting against her.

"I can't make it stop, oh fuck please! I'm sorry, I'm sorry, I'm sorry, I'm- Ah!" She cut her own sentence of with a shout, her body convulsing and her eyes rolling back. Zim used her weekend state to his advantage and slammed his appendage inside of a hole Dib hadn't realized that Sister possessed.

"Fucking filthy whore cant even wait to cum until after her brother!" Zim growled, grabbing her by the hair and pulling her head to expose her marked neck.

Despite his flat, useless, herbivore teeth, Zim was very quick to draw blood when he bit down on one of the purple marks. Sister screamed, and Dib couldn’t tell if it was the pleasurable kind from earlier or the pained ones he was more familiar with.

Zim’s hips slammed into hers, and despite his attempts to lick up the blood pooling in the wounds on her neck and lip, the crimson liquid continued to dribble out slowly.

“Sir, please, it hurts, it’s too much—!”

“That’s not the safeword, _pet_. Besides, I’m not done with you.”

Each word of Zim’s last sentence was punctuated by a sharp snap of his hips, and echoed by a whine from Sister.

“Do you want to make me cum, little slut?”

“Yes sir, anything!”

“Good. You feel so nice inside, my good girl. Even when you’re a disobedient. Little. Slut. You make me feel so good.”

Tears rolled down Sister's face, and Zim was quick to lick them away. Sister reached up to wrap her arms around him, and he didn't seem to be opposed to the action.

"I love you! I love you, sir! Please cum! Please cum for me!" She wailed as Zim continued to thrust into her relentlessly.

Zim growled- no, _snarled_ , and bit down hard on the meat of her shoulder, hips moving frantically before stilling completely, with his appendage fully sheathed inside of her.

After they stayed in that position for a moment, Zim pulled out of Sister. A white liquid dripped out of her and onto the sheets but Dib didn't pay much attention to it. He was more focused on Zim placing chaste, rapid kisses against Sister's bare skin.

“I love you, Zim.” Sister said, voice cracking and rough from overuse.

“Shh, be quiet. You screamed a lot, your throat has got to hurt.”

Zim kicked his pants off of his ankles, but pulled the purple shorts back up. He left Sister alone on the bed for a second, reaching into his backpack and locating a bottle of, presumably, water.

After taking a drink, he handed to bottle to Sister and climbed into the bed beside her, curling his body around hers protectively. Zim nuzzled his face into the hair on the back of her head, then leaned down to the marks and wounds he’d left to press gentle kisses in the center of each one.

“I love you. You know this, yes?”

“Mm-hmm. I love you too, Zim”.

“Good. It would not stand for me to love someone so unworthy that they cannot appreciate my affections!”

Zim’s words made Sister smile, a sweet little expression that Dib couldn’t get enough of, nor could he figure out _why_ he enjoyed it so much.

These two...would definitely have to stay under Dib’s watch for a while.

**Notes for the Chapter:**

> Local alien is confused by the concept of kinks, more at 11! 
> 
> Also Human!Zim has nipple piercings and this is a hill I will die on.


	3. Emotional Taboo

**Summary for the Chapter:**

> Dib and Zim incorrectly assume some things about each other, but it all works out for the best.

**Notes for the Chapter:**

> Original Zim and Irken Dib both get discovered the same way: through their own stupidity.

**[LOG DATE: 413612779 09:37 Local Time]**

_As far as observational science goes, I have collected all the data possible. These humans are particularly fascinating in their denial of any reasonable hierarchy, despite their clear dynamic of Overseer and Underling._

_For more detailed research, I will have to engage the pair of them more closely. Unfortunately this means I will have to approach the Zim human directly, as he seems to be the de facto leader and decision maker of the two._

_Perhaps he will be more receptive to the idea of Sister being involved in a hands-on study if he too is involved. I will proceed with this plan of action, and update these logs as necessary._

_Invader Dib, out.”_

**[MEMO CLOSED]**

Dib stared at the gentle white-mint light of his computer screen. He was finding himself particularly invested in this study, though he couldn’t be sure why. Perhaps something about human beings specifically was innately useful to the Irken Empire, and his natural intuition was picking up on it.

Because it certainly wasn’t his emotions getting in the way of his logic. Certainly not, even if he did find ever-increasingly often interactions with Zim and Sister enjoyable, that wasn’t why he chose them for this study. They were simply...available. Close, both to each other and Dib.

 _Compatible_ , even, to each other...and Dib.

Despite how obnoxious Zim could be, and how unhelpful sister was, Dib still found himself drawn to them.he excused it as them simply being interesting. They were fascinating subjects and that was why he wanted to look at them and touch them and be around them all the time!

That's why he snuck into their house and installed cameras in their personal domiciles. 

Just because they were interesting.

Them being interesting didn't explain the warmth that would pool low in his abdomen when he watched them kiss (he had learned that word from the Google, turns out the Library wasn't humans _only_ information hub).

When Dib and Zim were paired together for a class project, Dib took the opportunity to inquire about his participation on a hands on study session regarding his and Sister's relationship.

Zim was not _quite_ as enthusiastic about the concept as Dib had hoped, if the disgusted glare on Zim’s face was anything to go off of.

“Are you... _seriously_ asking me for _permission_...to bone my sister?!”

“Is that another ‘slang’ term I have not been made aware of?”

“YES, YOU FUCKING PERVERT!”

“Ah, now that one I know. I assure you my observation of you and Sister has nothing to do with personal gain.”

“Your... _observation_. Of us?”

“Yes.”

“So...you saw us... _last night_?”

“Yes.”

Dib had never seen a human drain their face of color so quickly, nor had he ever heard Zim speak so softly before. Dib was sure that he’d broken some arbitrary social contract with him, and mentally prepared accordingly for potential fallout. 

“You...you SICK LITTLE...I know I was...I was the one who...” Zim took a pause to breathe in and growl under his breath. “You _watched_ us. You inhumane little shit.”

Oh. Oh no. How could he have blown his cover like this? Where did he go wrong?!

"I-inhumane? I don't know what you're-"

"Shut up!" Zim hissed, grabbing Dib by the collar of his shirt. "You know what? We'll participate in your sick little voyeurism experiment as long as you keep your god damn mouth shut." 

Well! All things considered, that was easier than Dib had anticipated! Of course, now Zim knew that he wasn't human, which put the mission in jeopardy but Zim had agreed! Although Dib didn't quite understand what he meant when he was told to keep his "god damn mouth shut." 

He observed Zim informing Sister of the deal during lunch. This time, he was smart enough to bring a device that allowed him to tune into their conversation and drown out the rest of the cafeterias chatter.

“Weren’t you saying just yesterday that you didn’t want to hang out with him? What’s with the change of heart?”

“Oh, nothing just, uh...thought you could use some, y’know! Variety! We don’t want things to get stale between us, especially considering how much we’ve... _risked_. Being...together, and all.”

“Zim, honey, if you think I’m bored with you, you’re wrong. I don’t love you any less now than I did when we... _started_ all this.”

“Zim knows this, of course! Nobody as smart as my brilliant, brilliant sister could ever underestimate the attractiveness of I!”

“Of course not, Zim.”

“But...uh...we should still totally do it! For the fun of it! To spice things up!”

“I mean, I’m not saying no, just wanted to make sure you were really ok with this.”

“Zim would _never_ be so foolish as to invite an uncomfortable situation, and I would even more certainly never drag you into it!”

“What about the time you kept a frog in the bathtub and then it laid eggs?”

“That was ONE TIME!”

"Okay, well if you're sure then... fuck it. Why not. Let's let the new kid watch." Sister said. Dib made a note that Zim was hiding the true purpose of the observation from Sister. 

He also noted that they appeared very secretive about the extent of their relationship. He thought back to what Sister had told him the other day, about incest. Perhaps it was time to do some definition reading to piece together this mess.

sis·ter  
/ˈsistər/  
noun  
a woman or girl in relation to other daughters and sons of her parents.

rel·a·tive  
/ˈrelədiv/  
noun  
a person connected by blood or marriage

in·cest  
/ˈinˌsest/  
noun  
sexual relations between people classed as being too closely related to marry each other

sex·u·al in·ter·course  
/ˈsekSH(o͞o)əl ˈin(t)ərˌkôrs/  
noun  
sexual contact between individuals involving penetration, especially the insertion of a man's erect penis into a woman's vagina, typically culminating in orgasm and the ejaculation of semen.

Dib was beginning to understand the more... _taboo_ nature of Zim and Sister's relationship.

Somehow this made it all the more intriguing to Dib. Not only was he able to study such a strange method of reproduction (and apparently courtship), but he was getting to document an abnormal circumstance of it as well! Nobody had ever done that before!

Ok, maybe some human scientists had documented it. But they were human, and therefore stupid and bias. Not like Dib.

Among his normal scientific musings, and the usual repression of any icky, unnecessary emotions, Dib found himself wondering what Zim and Sister intended to do about their courtship if they could not experience all the steps of the human bonding ritual the internet had called “marriage”. If they could not fully complete the process, why would they waste time beginning it? The concept confused Dib, and he hoped his more adventurous experiments would help him to understand. 

Surely that was the only reason he was so excited to have his ~~favorite~~ human subjects alone with him in his base. That was why he was nervous that they wouldn’t like him without his disguise. Why he pushed through the painful spike in fear-related neurotransmitters at the idea of them running away.

When the door knocked, Dib opened it. When his ~~friends~~ subjects entered, he disabled the hologram functioning as his disguise, and adjusted his goggles. Despite Zim’s expression (shock, if he recalled correctly), Dib took the opportunity to initiate the first step.

“Shall we begin?”

Sister looked delighted, if similarly to her brother, shocked.

“Holy shit. Zim, is this my birthday present?”

Zim was utterly speechless.

"Jeez now I know what you meant by 'spicing things up' holy shit! Are you like, actually an..?" Sister grabbed Dib's face, examining it. The contact made his skin warm and made that terrible pool of heat in his stomach grow.

"Yes, I am in fact an 'alien.'" Dib confirmed. Sister squealed with delight and turned around to kiss Zim, still in shock from the revelation. The feeling of Sister's tongue in his mouth seemed to snap him out of his daze. 

"Thank you, thank you, thank you, thank you!" She squealed, although Dib wasn't sure what she was thanking Zim for. 

"Y-yes! You're welcome! I totally knew about this the whole time!" Zim said.

"As I was saying." Dib continued. "Shall we begin?"

He barely finished his sentence before being toppled to the floor. While Dib hadn’t gone into this interaction expecting to be anything more than an observer asking questions, he certainly wasn’t complaining that Sister was touching him, pinning him to the ground the way Zim had done to her. 

He also was not complaining when Zim lifted him up by the armpits and sat Dib back down on his lap. Sister reached a hand up to his goggles, slipping under the band on the side of his head, but not pulling them off.

“I wanna see your eyes.”

“O-oh! Ok!”

Once given permission, Sister eased the heavy chunk of metal and glass off of Dib’s head and tossed it onto the couch. 

“Whoa, they’re compound.”

“Hah! Of all the alien creatures we could have stumbled across, of course we got the _fucking insect_.” Snarled Zim, laughing in between breaths.

“Do _not_ insult my people, primate.”

“Oh? What are you going to do about it, little alien?”

"Ladies, you're both pretty now can we PLEASE get to the good part already? I'm fucking soaking and I really _really_ need somebody to touch me." Sister said, running her hand up Dib's thigh. The feeling made him sudder and something inside of him... unfurled. 

Literally.

He was unfamiliar with the situation that was going on in his pants but Sisters reaction was positive.

"Oh there we go." She crooned, rubbing Dib's bulge in a way that made him shudder.

"Horny little alien perverts already hard." Zim grumbled, slowly grinding against Dib, a bulge forming in his own pants as well.

"I-I'm not so sure the two of you understand what todays experiment entails!" Dib said, although the more the siblings touched him the less convinced he was that he wanted them to stop.

"Of course we know, silly! We're here to fuck your brains out! Give you a taste of what it means to be human." Sister purred.

Dib’s retort was silenced when Sister reached into his pants and yanked them down. She wrapped her hand around whatever was _moving_ down there, and pulled it into view.

It was squirming, a dusty cobalt-blue like his eyes, and it was _slimy_ , leeching fluid from every pore. It resembled a long, segmented tube that tapered at the end, just like his tongue, but thicker. 

Dib vaguely recalled a drawing he’d seen as a smeet, an anatomical study he’d caught a glance of before it was confiscated and the classmate responsible for the sharing of such ideas exiled. Dib realized in a moment of sudden clarity why such things had been forbidden to talk about, if his people knew about _this_ , they’d never do anything else! 

His thoughts were silenced, along with his breathing, when Zim took his head in his hands and turned him to the side so he could press their mouths together.

Dib wasn't sure what to do but hold still, however he couldn't stop the moan that he let out when Zim's tongue swiped across his lip. At the same time, Sister wrapped her hand around his cock, twisting her hand up and down on it the same way he had seen Zim doing to himself.

He could feel Zim's hard on pressed up against his ass, the feeling flooding him with what he would later identify as arousal. Sister's hand reached below his appendage, searching for something and she gasped when her fingers only found a wet, pulsing, hole.

"Oh my God. He's got a pussy too." She whined, dipping a finger into his hole while she used the other hand to jerk him off.

Zim surprised both of them by shoving Dib forward, on top of Sister. The motion forced her finger all the way inside his virgin hole, making him whimper.

Zim yanked Dib's pants down further, giving Sister a signal that Dib couldn't quite see, to remove her own pants as well.

Sister distracted Dib while Zim busied himself with manhandling Dib’s hips into a more agreeable position. Dib let his mouth hang open as Sister kept two fingers inside of him, using her palm to squish his dick against his belly. Zim caught her eyes, and she pulled her hand back, leaving Dib to whimper at the loss of contact.

Sister cupped Dib’s cheek with her clean hand, and without warning stuck the fingers that had been inside of him moments before into his mouth. When his tongue darted out to touch them instinctively, she grabbed hold of the thing and gently tugged it past his lips. 

“Zim, holy shit, look, his tongue looks like his dick!”

“Good, then you won’t have an open mouth to complain with!”

Sister took this as instruction to suck Dib’s tongue into her mouth, filling his mouth with her much smaller and warmer one. Just when Dib was getting used to the _fantastically_ foreign sensation, he felt something hot and hard pressing into the hole that Sister had been touching.

He screamed into her mouth when Zim fully sheathed his cock inside of him.

Sister moaned and stroked his head comfortingly. He whimpered as Zim pulled back and then thrusted in again.

"That's right, take Zim's cock you filthy alien pervert." Zim growled. Dib was too lost in the sensation of his virgin hole being stretched to notice that he had spoken at all.

Sister pulled a hand away from Dib's face to reach down and finger herself, moving in time with Zim's thrusts. 

"If you're going to be such a needy little whore, just fuck him instead of wasting energy touching yourself." Zim commanded. 

"Yes sir." Sister said and guided Dib's cock into her cunt.

When she finally coaxed the tip of the wriggling appendage into her body, Zim gripped Dib’s waist and snapped his hips up, _hard_. The motion forced Dib’s cock fully into Sister’s pussy, he transition seamless from the absolutely colossal amount of liquid leaking from both of their cores. 

Dib moaned, gripping the carpet with shaking hands as Zim fucked him. Sister continued running her hands over his head, and Dib’s moaning only got louder and more desperate when her fingers brushed his antennae.

“Hey Zim, look, I think he likes this!” Sister said, pinching the base of the alien’s insectile sensory organ. Her thumb and forefinger ran agonizingly slowly up the thing, making Dib shake and squeal the whole way.

"Of course he does! How could he not enjoy being fucked by the likes of us?" Zim said.

"No, I mean _this_ ," she said and repeated her assault on Dib's antennae.

Zim opted not to respond, instead he just grabbed an antennae and gave it an experimental yank. It wasn't particularly rough, he was mostly just testing the waters. But the feeling of it still made Dib scream.

Sister tilted her hips upwards and wrapped her legs around Dib and Zim, pulling them in and urging them to go deeper.

Zim gave her what she wanted, pushing his hand up against the small of Dib’s back and pushing him down onto her body. Her arms wrapped around Dib’s neck on impulse, and Zim laughed darkly in pride. Zim and Sister took turns licking and sucking at a spot on Dib’s neck, staring in wonder and arousal at the dark bluish-green bruise they left behind. 

With Sister’s tongue no longer occupying his mouth, Dib let his own tongue hang loose past the side of his teeth, drool dribbling off the thing and onto Sister’s bare chest. 

Zim wrapped a threatening hand around Dib’s throat, but instead of snapping his neck like Dib expected, he just used the angle to force Dib’s head up, exposing where his Adam’s apple would be if he were human. 

“What do you think, oh dear sister-of-mine? Shall I put some more pretty bruises on his neck to match yours?”

"Yes! Fuck, let's ruin him!" She moaned. 

"That's what I thought." Zim said, and bit down on the curve between Dib's neck and shoulder. His voice was hoarse from screaming and moaning but that didn't stop him from whining as the siblings bit and sucked on his flesh.

"Fuck! I'm gonna cum soon!" Sister said. Zim doubled his speed, and Dib reached an incredible euphoric peak, his cunt clenching and his cock draining.

"Shit, looks like you beat me to it Space Boy." Sister teased. Even though Dib had cum, neither Zim nor Sister allowed him a break. They just continues to fuck his spent, exhausted body until they too had reached their orgasm.

Dib was not used to the feeling of the sticky, warm feeling of _human_ inside of his body, nor was he used to the feeling of spilling himself into one. But even as he let this pair of, foul-mouthed, antisocial, deviant, alien siblings use his body for their own pleasure, he found himself _comfortable_ for once in his life. 

And once Zim had pulled out, and Sister had let Dib’s spent cock slip back into his body, the two of them pulled themselves onto the couch, and they curled up together as they had the night before, this time with Dib in between them. 

Maybe, just maybe, Dib could get used to the Earth.

**Notes for the Chapter:**

> Zim: *finds out the kid who’s been stalking him is an alien, his girlfriend/sister is a xenophile, and he might be one too*  
> Zim: That’s how it be on this bitch of an Earth.


	4. Impromptu Interview

**Summary for the Chapter:**

> The afterglow can’t last forever, and Dib seems determined to bring down the room whenever possible.

**Notes for the Chapter:**

> Fluff! Backstory! Plot! D I A L O U G E!

Irkens don’t need to sleep. Maybe a couple hundred millennia ago, before the first Tallest completely mechanized the planet, when smeets used their teeth for much more violent activities than tearing into food, perhaps they did. But the introduction of PAKs had eliminated the need for sleep, and nowadays having enough spare time to waste on such luxuries was reserved for only the highest-ranking of Irken Elites. 

Dib was not an Elite.

Despite having gotten somewhat used to the strange ways humans spend their time, it still surprised Dib that his new confidants would forego bodily upkeep to waste time sleeping on each other, especially considering they’d chosen to do so on _his_ couch.

Not even the incessant rumbling of their bellies was waking them up. The noise did, however, prevent Dib from focusing on any reasonably productive task, and evidently the hormones his humans had released during their most recent... _interaction_...had infected Dib with a sickening feeling somewhere in his guts.

Cursory research suggested the feeling was a “crush”.

It was sort pf alarming how quickly he'd grown fond of these humans. These stupid, weak, squishy, _adorable_ humans. He also had to admit the noise that their stomachs were making was kind of spooky too.

But, much to his relief, it turned out that the rumbling only meant that they were hungry. 

Dib was overwhelmed with the urge to feed them, and take care of them. It was an unfamiliar feeling, one that he was almost certain had been brought on by last nights Activities. 

How does one feed a human? Dib wasn't even sure if he kept any food at the base.

He kept food for _himself_ obviously, but he wasn’t sure if humans could eat Irken food without dying, and he didn’t have any other test subjects readily available! Before he could send himself into a panic over the possibility of his humans potentially starving under his care, Dib was interrupted by his beloved, terrifying SIR Unit.

“Hey idiot, if you’re done being a creepy weirdo there’s a new video game and I want it.”

“Ah, perfect timing! If you’re going out, acquire some food for the humans, something they can reasonably eat.”

Gaz grumbled, but agreed. Dib wondered if it had really been worth it to rewire her the way that he did, but despite her more abrasive nature, his ~~unlicensed~~ upgrades had made her much more dangerous as a guard. 

She returned with a greasy box labeled “pizza” and a brand new, most likely stolen, game. The box hit Dib in the head when she threw it at him, and the resulting yelp of pain woke Sister up. She seemed excited about the food though.

"Oh fuck yeah, pizza time baby!" She said, stretching. The action made her bones pop and crunch in an alarming manner but she didn't seem to be hurt by it. "Zim. Zim! Wake up sleeping beauty it's time for breakfast!!"

Zim only grumbled and rolled away from her. Sister leaned over him and gave Dib a wink (what did that mean again? He could never seem to remember human social cues).

"Zim baby, this is your last chance." She said, gently stroking Zims hair.

"You can't make Zim get up." He grumbled. Dib found his voice, rough with sleep and laced with affection, to be a _very_ pleasurable sound.

"You leave me no choice, my love!" Sister said dramatically before her hands shot out to Zim's abdomen. She was... poking him? Repeatedly? He screamed, and burst into a fit of giggles.

The laughter mixed with shrieks and Zim eventually grabbed her by the wrists and breathed harder for a second. After a moment, Sister leaned down to kiss Zim (but why? They seemed so uncomfortable even hugging each other outside of Dib’s base, and from what he could tell, kisses were more intimate than hugs).

“Now that you’re _awake_ , we have pizza for breakfast.”

Zim gave her an indecipherable look and took a massive bite out of a slice of the stuff. Dib approaches them slowly, as not to startle them, with the intention of sitting beside them on the couch, but chickened out at the last second and simply stood behind Sister awkwardly.

“You, Alien! Cease your hovering and sit.”

Dib, the poor frightened fool, immediately sat on the floor.

"No, you goober, he meant come sit with us! Y'know, on the couch?" Sister teased. She patted the empty space next to her and Dib scrambled to climb onto the couch before the offer was rescinded. 

Sister gave a pleased hum and gently bonked her shoulder against his. Zim handed her a slice of pizza which she gratefully took, thanking him with a kiss on the cheek.

Perhaps now would be a good time for Dib to begin asking them questions, now that they were comfortable.

“I would like to know some things about you.”

“Oh? Like what?” Asked Sister. 

Zim apparently was back on edge, one of his arms sliding up to Sister’s waist and pulling her closer to him...and _away_ from Dib. Zim stared suspiciously at Dib, who lowered his antennae in submission. Dib was not a threat, nor did he intend to be, and for some reason he wanted desperately for Zim to understand that. 

“When will the haze wear off?”

“The...haze?”

“Yes. You humans each have a distinct smell, and it changes when you do certain things, like the ones we did yesterday.”

“...yeah?”

“It had a haze to it, a warm sort of fluffy mush in the brain. I presume this is a side effect of your pheromones, and I’d like to know how long it will take for my mental state to return to normal.”

“...oh my god.”

“What?”

“Aww! Zim, did you hear that? The alien kid’s got a crush on us! He sounds just like you did when you confessed to me!”

"Don't compare my grand love confession to this! I was far less confused about my feelings for you..." Zim grumbled and buried his face in her neck.

"Are you sure about that? Because I remember it very differently." Sister said, turning her head at an uncomfortable angle to kiss Zims hesd.

"Actually, I'd like to know about the origin of your relations. I've come to understand that it's very... _unusual_ for humans sharing the Sibling status to have a sexual relationship." Dib asked.

"Well, it's kind of a long story." Sister said.

"A very long and beautiful story that Zim will tell!" He exclaimed, pulling his face from Sister's neck.

"And which I will periodically correct because this goofus likes to make it even more dramatic than it actually was."

“We have been isolated since birth, only with each other to turn to! Humanity has produced nothing but worms, unworthy of the company of Zim!”

“Nobody could stand to talk to us because ‘don’t understand boundaries’ and ‘are really annoying’ so we just said ‘fuck em!’ and kept to ourselves.”

“The especially stupid ones picked fights in a feeble attempt to prove themselves, only to run away like rats once they realized they wouldn’t be able to best me!”

“When we were in first grade, Zim broke a middle schooler’s nose because he was teasing us, so people left us alone.”

“It took years to sort out our inevitable romance, but we broke through each other’s perceived barriers and learned to enjoy ourselves together, without care for the thoughts of outsiders!”

“Puberty hit us like a brick.”

“So now we live our lives together, in secret! I’ve staked my claim on her, and nobody in the world was foolish enough to challenge me, until _you_.”

“Zim gives me hickeys a lot and everyone kinda knows what’s going on but nobody talks about it since it makes them uncomfortable, and since nobody’s actually seen us doing anything too intimate, there’s not enough evidence to confirm any rumors.”

“We live a life on the edge with nothing but our flawless intuition and genius intellect.”

“We just keep to ourselves because nobody else is any fun to be around.”

It was a lot to take in all at once but Dib thought he understood it for the most part.

"I see. I have several follow up questions if you don't mind answering them?"

"Yeah go for it! I've never really gotten a chance to brag about how much I love this dork so, I'm happy to do a little interview."

"Zim agrees!" 

"Good! Now, what exactly is it that makes the nature of your relationship so illicit? Why are Siblings not permitted to breed with one another?"

"Fuck, I thought these were gonna be fun questions like 'where did you go on your first date' or 'what was it like to have sex for the first time?'" Sister let out a little nervous laugh, to which Zim gave her a comforting squeeze and took it upon himself to answer the question.

"When humans inbreed the resulting children often have terrible physical deformities. It is very bad for the species as a whole!" Zim said.

"I'm honestly not sure about the social stigma aspect of it. I mean, who better to love than someone you've known since you were born, right?" Sister said and Zim nodded in confirmation. 

"Is there anyone who's ever 'caught you in the act' so to speak?" Dib asked, making careful note of their reactions. 

"Well... there was the time Red caught us kissing in the attic after dinner on Christmas." Sister said, bringing her fingers up to her mouth to chew on her nails.

"Zim feels ill just thinking about it." He said, in a surprisingly soft tone.

"I'll tell the story then." Sister said. "If you want to hear it."

"I do!" Dib said, and immediately chastised himself for his excitement.

“Well, like I said, it was Christmas, that’s a really important holiday for a lot of humans, after dinner. We were 13, staying at our aunt and uncle’s place, and we ended up sleeping in the attic.”

“You’ve mentioned this Aunt person before, yes?”

“Yeah, Aunt Miyuki. She and Uncle Spork travel a lot, so Red and Purple are on their own at home most of the time.”

“Ah.”

“Anyway, we were in the attic at night, and we thought everyone else was asleep, so we got into bed. Y’know...together.”

“I see.”

“Anyway, Red came up, and he caught us. We had our clothes on, thank goodness, but it was still way too intimate to be normal sibling behavior. He told Purple, they assumed we were just stupid kids who hadn’t been taught any better, so they started teasing us about it.”

“Oh...”

“That’s... _probably_ the reason our cousins are such jerks to us. I mean, they were pranksters before, but when we were little it was mostly harmless stuff, like switching the salt and the sugar in our kitchen. After that though, it started getting...malicious. Zim’s _really_ allergic to soy, and lima, and...well a lot of beans, and they started putting that in our food when they cooked for us.”

"I had to be taken to the hospital on more than one occasion." Zim said, surprisingly somber compared to his usual bravado. 

"But the weird thing is that they never _told_ anyone about it. At least, I don't think they did. If they told aunt Miyuki she would have told our mom and our mom would have killed us so..."

"She would _kill_ you?!" Dib gasped. Now he fully understood why Sister and Zim insisted on keeping their relationship as private as possible. 

"Well, maybe not _kill us_ kill us but-"

"No, whe would most certainly terminate our existences." Zim interrupted. 

"Yeah. She's a pretty... _traditional_ woman. I had to tell her that I have a boyfriend who goes to another school so she wouldn't get suspicious about all of the hickeys."

“Zim is not pleased with this situation but it is preferable from being eliminated.”

“Or separated.” Sister chimed in. Dib did not miss Zim’s already protective hold tightening at her words.

“I...I believe I understand.” Remarked Dib, thoroughly overcome with some disgusting newfound _emotion_ he was very unused to. “In that case, I have a proposition for the two of you.”

“What.” Growled Zim, teeth on display in a snarl.

“I will help you keep your secrets. I have technology capable of making you practically invisible to the public eye. And I’ll... _participate _...in your endeavors if you so wish.”__

__“I do wish.” Said Sister._ _

__“...and in return, you will come here on a regular basis, and you will allow me to study you. I assure you, none of my experiments are fatal or have long-term side effects, but they will not all be as enjoyable as this last one.”_ _

__Zim and Sister looked at each other and nodded. Zim stuck his flat palm out, fingers together._ _

__“Deal?”_ _

__“Deal.”_ _

**Notes for the Chapter:**

> Surprise bitch it’s angst.
> 
> Also yeah, that’s why Red and Purple are so cruel to Zim in this universe. I mean, a couple of 18ish-year-old boys walk in on their little cousin frenching his sister? Yeah, that’s not gonna end well.


	5. Heat of The Moment

**Summary for the Chapter:**

> Well it isn’t the sort of gentle arousal he’s used to, but Dib is certainly enjoying this new intensity.

**Notes for the Chapter:**

> It’s not Tuesday.

After a few weeks of sneaking around and mating with a pair of aliens, Dib would have thought he’d know their routines by now. But no, his new companions were wild, chaotic, unpredictable. 

And he _loved_ it.

He could never tell if he’d return from an errand and find them curled up asleep on the couch being cute, play-fighting over who got to control the tv remote, or naked and pressed up against each other. No matter what it was, they were always ready to invite him to join.

For some reason though, he’d been finding himself more and more insatiable lately, and the feeling only seemed to increase with time, and perhaps even more so, exposure to his lovers.

Today had been especially bad. He was so aroused that he'd skipped school to stay home and try to alleviate himself. But it seemed that no matter how many ropes of hot sticky cum he painted his hands with, he was never satisfied for more than a moment.

Zim and Sister had been alarmed by his absence, so they decided to check up on their little green lover during their lunch period. 

What they found when the entered Dib's base was one of the most erotic sights they'd ever seen. Dib was frantically fingering himself with one hand and yanking on his engorged cock with the other.

Sister had kicked the door shut and practically skipped over to him within seconds, while Zim smirked lustfully and sauntered over. Dib had barely registered the pair’s presence when he felt Sister’s hand replacing his own, the one he’d been fucking.

“Couldn’t wait for us to get home, huh?”

“Please, I don’t know what’s happening, it’s too hot, I can’t think...”

Sister silenced him with a kiss, and Zim’s hand joined hers in jerking off their alien bedmate, whispering filthy words to him while he was distracted with Sister’s lips.

“You’re so cute when you’re desperate and needy. Already begging too, how nice. But now, don’t stop on our account.”

Dib rutted against their hands, nearly crying from the relief he felt from his lovers touching him. When Sister pulled away to remove her top Dib whined like a forgotten puppy.

"Be patient Space Boy, I'm gonna give you what you need." She said, tossing her shirt aside and working on yanking her skinny jeans down. 

Zim stroked Dib's cock with one hand, and fingered him with the other, he was trying to hit all the bases while his sister undressed. Their poor little alien was suffering. And what kind of a boyfriend would Zim be if he just sat back and let it happen?

Dib's cunt tightened around Zim's fingers when the boy took one of Dib's antennae into his mouth and sucked on it. He came, yet again, but it still wasnt enough

Sister was very clearly enjoying teasing Dib, if the overwhelming smell of her arousal was any indication. The sight of her bending over to pull off her panties was enough to break whatever was keeping Dib under control, and he pinned her down with reckless abandon. 

“Whoa, what’s gotten into you?”

“I-I don’t know, I just can’t stop...I _need_ to fuck you. I _need_ to cum inside you, I can’t think about anything else...!”

“Shit, if you wanted to be on top you should have just said!”

She wrapped her legs around his waist and pulled him in. He collapsed on top of her but she didn't seem to mind the extra weight, especially not with Dib's cock squirming against her wet lips. 

It was less like a thrust and more like a twitch when he entered her, but it didn't matter. He was _finally_ getting a sliver of relief and that was all that mattered.

Dib shook violently at the contact, cerulean tentacle thrashing wildly as he tried to force the thing deeper into Sister’s pussy. Despite the frantic, apparently involuntary, movement of his cock, and the slimy slick dripping off of it, Dib still managed to force himself entirely inside of his _very_ willing mate. 

Thin, tri-fingered hands found purchase on Sister’s hips, claw-like fingertips digging into her flesh like a hot knife through butter. The wounds were shallow, they didn’t bleed, but they still stung enough that even through the hormonal haze, Dib still felt the need to apologize once his partner whimpered.

Unfortunately for Dib, once he started talking, he lost the control needed to stop.

'I-I'm not sure what this is but- _fuck_!" He moaned as Sister squeezed herself around him. "I love it! It was torture before you got here but now? N-now I don't want it to end!" 

"It's like this is your first time being horny!" Zim scoffed, sliding his fingers back into Dib, curling and pumping them until he found the spot that made Dib squeal. Dib didn't have the wherewithal to give a coherent answer.

"I bet nobody fucks you like this on your home planet." Sister teased, rolling her hips against his frantic thrusts.

"Irkens don't do _anything_ like this!" He groaned, his cock had brushed up against her cervix, inspiring a new wave of heat and need.

“Oh, honey we have _so much_ to teach you then!” Said Sister.

“Indeed!” Added Zim, punctuating the addendum by licking a stripe from Dib’s collarbone up to the tip of his antennae.

Dib wiggled his hips in an attempt to get even more friction out of his position. Since he was pressed between both siblings though, he wasn’t able to move himself much, but the slight change nearly made him start drooling. 

“Stupid alien, didn’t even know how to touch himself properly before us. Zim is going to _ruin_ you.” Whispered Zim, his breath leaving hot flashes on Dib’s skin that quickly turned cold where his saliva still lingered. 

Dib moaned. Zim smirked at that, and Sister seemed adamant on teasing him about it.

“Oh, now _that_ was a good noise! Do you like that idea, having us two absolutely wreck you tonight?”

"Yes! Please, destroy me!" Dib's response elicited giddy smiles from both siblings. When Zim pulled his fingers out of him, Dib nearly cried. Well, not nearly. He sobbed at the sudden emptiness. Zim, the teasing bastard, just laughed.

"So needy that you can't handle not being touched by me?" He asked. Dib couldn't find the words to respond. Zim _was_ kind of right. This neediness was incredibly unusual. once he got his wits about him he would have to do some serious reading.

Before Dib could even think about developing a theory to explain his own behavior, he was distracted by the feeling of Zim's tongue poking at the entrance of his hole.

Dib _screamed_ at that. He’d only just barely gotten used to the feeling of his humans’ fingers inside of him at this point, and suddenly Zim was opening a world of new, filthy ideas. 

Dib was thoroughly enjoying every single one of them.

The new sensation was only heightened when Zim wrapped his hands around Dib’s skinny thighs and moaned into his hole, the mix of Zim’s tongue and the vibrations of his throat eliminating any semblance of thought from Dib’s mind. 

Sister whined, and snapped her hips up to force Dib’s cock back inside of her body. He almost let his hands fly to her hips again, but thought better of it and buried his claws in the soft carpet beneath him.

“Oh holy shit, you gotta try this later, even his pussy juice is sweet!” Barked Zim, taking only a momentary break to breathe before plunging his tongue back into the aforementioned alien’s body.

Sister gave him a mischievous grin.

"I bet your cum tastes like candy." She whispered. "I'd _love_ to try it." 

Dib dropped his entire body completely on top of hers, diverting all of his energy into fucking her as hard as he could while getting tongued from behind. The dirty talk was new to Dib, even newer than the concept of sex itself, and he found that the more his lovers spoke the more aroused he got.

“Hurry up, spaceboy. The faster you go, the better it’ll feel, I promise. If you’re still conscious after you cum inside me, maybe I’ll suck you off then.”

Dib bit his lip and nodded, squeezing his eyes shut to keep the pleasurable tears from falling out. Sister was apparently having none of this, as she pried his mouth open with her thumb and kissed him hard.

Somehow, Zim’s tongue in Dib’s slit and Sister’s tongue in Dib’s mouth made _almost_ the exact same movements. The parallel was not lost on Dib, though he didn’t bother thinking on it any more than how _good_ it felt. 

His cock was leaking obscene amounts of translucent cobalt fluid, so much so that Sister’s body was having trouble keeping it all inside. Every thrust Dib made forced more of the slick out of her and onto the carpet, and his cock just kept replacing the lost fluid with _more_. 

Dib was sure it would be a pain to clean, but it felt way too good to stop.

He hadn't even realized he was practically screaming until his throat was raw. He wasn't sure what it was that pushed him over the edge, but before he could even processes what was happening he was cumming. 

If Sister's cunt was full before, it was _stuffed_ now. Every thrust forced out a gush of fluid that was definitely going to leave a stain.

Clearly, Dib wasn't the only one enjoying himself; Sister gasped, her back arching up off the ground. Her legs shook around Dib's waist, and her eyes rolled back. Dib was so caught up in the pleasure exploding from his cock that he hadn't even registered that the tongue exploring his cunt had been replaced with Zim's cock. He was grinding against Dib's exposed (and _soaked_ ) cunt, but never quite going inside.

Dib struggled to keep his cock inside the more submissive of his mates. The amount of fluid he was spilling into her was enough that it was physically forcing his cock to slide out. Dib wasn’t even sure _why_ he wanted to badly to keep inside her as he came, all he knew was that his body wanted him to spill every drop he had into her wet, willing hole. 

Despite Dib’s desperate attempts to keep his cock inside of her, she eventually slid out of his grip and fell to the floor. Without the upwards tilt of her hips using gravity to her advantage, the cerulean liquid she’d been stuffed with leaked out of her body, short gushes dripping out as she breathed. 

Dib was _almost_ disappointed that her womb wasn’t big enough to house all of his cum, but he was very quickly distracted from that once Zim slipped his cock fully inside of him.

“Fffffuck, he’s still just as tight as ever! Why don’t you clean yourself up while I finish him off here?” Growled Zim, smirking through every word.

Sister made no move to get up, instead opting to push gently on her swollen belly and joining her male counterparts in watching even more fluid drip out.

“Nah, I’m gonna sit here and wait for round two. Give the little swimmers a chance, y’know?”

"You've been on the pill since you were twelve but _whatever_." Zim said, pushing Dib so that his chest and head rested against the floor while his ass was pointed up in the air. 

Dib was oddly focused on the comment that Sister had made. He'd gotten quite a bit more... _knowledgeable_ about human mating practices since his first Encounter with the siblings, but he still wasn't entirely sure of the ins and outs of breeding, or the meaning of most (if not all) colloquialisms and metaphors.

But using what he'd learned he was _pretty_ sure that Sister was implying that she wanted Dib to... to impregnate her.

 _Fuck,_ that thought was terribly arousing.

Dib wasn’t sure wether the involuntary twitch of his cock was because he liked the new position, or the feeling of Zim’s cock fucking him _hard_ , or if Sister’s little comment made him _way_ more into it than he’d thought. 

Either way, Dib was thoroughly lost to the pheromones and sensations. Even with his face being smushed into the carpet by the hand of a former rival, he was moaning and _smiling_ through his actions. 

Sister was watching her brother and her alien with an intensity Dib had rarely seen. Her eyes darted back and forth between the two of them, but the heat behind her glare never left.

Wait.

 _Heat_. That’s what this was. Dib was struck with a realization that he’d given in to the most absolutely basic and fundamental instinct he had. The need to find a mate and _fuck_ them, to stuff them with his seed until he had none left to spill. 

No wonder he was enjoying the idea of making little hybrid smeets with these two.

Dib wasn't even aware that Irkens had heats. He'd heard rumors many years ago but those were quickly snuffed out before they could catch on. 

Somewhere in the back of his mind that bothered him, it planted a single seed of doubt in his mind.

But that was not the seed that he wanted to focus on right now. Hell, he couldn't have focused if he tried. All he could pay attention to was the bruising pace that Zim had set and the erotic gaze that he was receiving from Sister.

He made a motion to reach out to her when he saw her own hand snake its way down to her blue cum-covered clit. In Dib’s head, the idea was to let her use his hand to get herself off, like she’d done to him so many times. 

Dib only succeeded in going from laying on his elbows to having the entire left side of his face buried in the carpet as Zim gripped his hips and snarled behind him. 

The hot liquid Zim spilled into Dib’s insides was satisfying in a way he’d never experienced before, but it _still wasn’t enough_.

Zim pulled out, letting both Dib and himself fall to the floor. He seemed like he thought the session was over, but Dib crawling over to kiss Sister again proved him very wrong. 

Dib had been stuffed with cum by Zim, and spilled copious amounts of his own into his sister, but even so there was liquid dribbling off of the tip of still-writhing cock.

“Again? Please?” He whispered with a voice he’d almost broken.

"Jesus Christ, Space Boy! You're insatiable!" She giggled, then her demeanor changed, going from silly to serious in a heartbeat. "Fuck me, Dib. Fuck me like you mean it."

Shit, you didn't have to tell him twice! Dib was already inside of her before she even finished her sentence. Fucking her while her insides were coated with a thick layer of his cum was probably the most pleasurable experience he'd ever had. Each thrust was practically its own orgasm.

Dib couldn’t help himself when he buried his face in between her neck and chin. He couldn’t help himself when he inhaled the smell of her, all hormones and sweat. He _especially_ couldn’t help himself when he slid his segmented tongue up her neck and bit down _hard_.

The half-scream, half-moan noise she made was almost enough to make both Dib _and_. Zim cum. 

Instead, Zim’s hand returned to his already half-hard cock, lazily jerking himself off at the sight of his alien lover delirious with sex and fucking his sister into the floor. 

Dib’s mumbled, almost incoherent words didn’t exactly hurt the mood either.

"So good, want to- to fill you up with my smeet! So warm! So-ah!" When Sister's orgasm hit, Dib was left utterly speechless by the sensation. It was like her body was _begging_ for him to impregnate her. He almost didn't notice the feeling of his cock swelling up inside of her.

Almost.

"Holy shit." Said Zim. He had a perfect view of Dib's rapidly engorging cock seeking shelter in his sisters cunt. She sure didn't seem unhappy about the situation if her pleasure filled moans and shaking orgasm were anything to go off of.

The coil finally snapped and Dib felt yet another gush of slick spilling out from his dick. The rush of relief at the hot, sweaty, needy feeling leaving his body distracted Dib for a moment. The moment was apparently long enough for Zim to finish himself off, managing a second orgasm at the view he’d been given. 

It took Dib a second to catch his breath, to come down from his incredible high, before he realized something unfortunate.

His swollen dick was now entirely stuck inside Sister.

And he had no idea how long it would take to deflate.

"D-Dib? What's uhh... What's goin' on on down there hon?" Sister asked. She tried to scoot out from under him but the knot made it impossible.

"He knotted you like a fucking dog!" Zim yelled, suddenly finding the situation hilarious. Sister stared blankly at the ceiling for a moment while processing that information, before she too began to giggle at the utter absurdity of the situation. Even Dib couldn't help but laugh with the siblings. Once the giggles died down, Sister spoke up.

"Hey, Dib? Quick question," she said. "What the hell is a 'smeet?'"

Dib choked on nothing. He had nearly forgotten what he'd said in the heat of the moment.

"W-well a smeet is... I suppose you could think of it as..."

"Spit it out Space Boy" Zim said, though his voice was muffled since he had rolled onto his stomach and buried his face in the carpet.

"It's the Irken equivalent of a human child!" He shouted, immediately burying his face in Sister's hair to avoid the shame of having to look her in the eyes.

"Aww! Space Boy has a breeding kink!" She yawned, shifting underneath him as best as she could without hurting herself on Dib's knot. "That's so cute..." She muttered, eyes fluttering closed.

And just like that, both of his humans were asleep on the floor. It was sort of cute in its own way that they were so ready and willing to pass out on any half suitable surface. With his cock stuffed inside one of his lovers and no way to move, he decided that perhaps he'd join his humans and rest with them.

He fell asleep feeling all sorts of warmth.

**Notes for the Chapter:**

> “But how does Zim know immediately that it’s a knot?” I hear you saying. “Are you two weirdos gonna end up veering into beastiality territory with this fic?”
> 
> And to that I say no, we don’t feel like it.
> 
> The only logical answer is that human!Zim is a furry.


	6. An Uneggspected Development

**Summary for the Chapter:**

> Heat lasts more than two rounds, c’mon. Also there’s some plot there somewhere.

**Notes for the Chapter:**

> More kinks!!! Why? Because fuck you this is our fic and we do what we want.

If Dib had 10 monies for every time he’d woken up overheating and insatiably aroused with a foreign swelling feeling in his dick, he’d have 20 monies. That isn’t a lot, but it’s strange that it’s happening again. 

This time though, the feeling was a lot more intense, a lot more sudden, and a lot more _visible_.

And as much as Dib enjoyed the sight of a softball-sized sphere slowly moving through the tentacle between his legs and into the waiting hole of the person he was tied to, he wasn’t sure that his human mates would be quite as receptive to the concept.

Even if the body of the mate he was currently still knotted inside was reacting _very_ intensely.

Sister's pussy squeezed his cock so tightly that he wondered how it wasn't painful for her.

It was cute though, even when she was unconscious her body still reacted positively to his. He'd have to write this down once he figured out what exactly was going on. And once he could, y'know. Move

Dib watched the object in his cock inch toward his mate with laser focus. He didn't even bother trying to muffle his own whines of pleasure.

Surprisingly, the noise didn't wake Sister. 

But it did wake up Zim.

“What th’ fuck are you doing awake, it’s like two in the goddamn—oh.”

Dib frantically shushed Zim, gesturing to his still-sleeping sister. The action did silence Zim, but it also drew attention to the bulge moving down Dib’s cock. It caught Zim’s eye, and made him smirk. 

And then he went and poked it.

The touch was anything but sexual, it was childish curiosity and obnoxious teasing at best. Still, the feeling of Zim’s fingertip touching the _thing_ through the sensitive flesh of Dib’s cock was electric.

“Nnngh...don’t do that! I can’t...I-I mean, I’ll...the noise will wake her up!” Protested Dib, weakly.

“Oh please, as if this whatever-it-is going into her won’t?”

"I suppose you're right, b-but-"

"But what? Wake up sleepy head!" Zim shouted, startling Sister out of her peaceful slumber.

She groaned in annoyance but was distracted from the rude awakening by the feeling of Dib's cock twitching and squirming inside her.

"I just had the most wonderful dream... You were there, and you were there!" She joked, wiggling her hips, subsequently pushing herself far enough down on Dib's cock that she could feel the bulge press against her already stretched hole. Her eyes snapped open and she looked down to the place where their bodies joined. "Holy shit."

“Holy fuck, is that what I think it is?!” Sister exclaimed.

“Th-that depends, on what you...what you think it is?”

“Well I _think_ your insect-slash-alien dick is putting an egg in me.”

“That would...uh...that would appear to be the case!”

“Fuck, I don’t know wether to freak or be turned on.”

“I would prefer the latter!”

Zim took the opportunity to pull his sister into his lap, fondling her breast with one hand and moving her hair out of the way to kiss her with the other.

“Zim would _also_ prefer the latter.”

"Horny it is then." She sighed against Zim's mouth. 

It was most likely entirely coincidental that as soon as he got vocal confirmation that his mate wanted to carry his eggs that _another_ egg pushed up from the base of his cock, behind the one currently pressing against Sister's pussy. But Dib wasn't sure he believed in coincidences. After all, there's a reason for everything.

Sister hissed when the egg bulge began to push more insistently at her unwilling hole. Dib apologized, but Zim decided to take action. He reached around to rub his sisters clit. Perhaps, if he made her cum again then her body would relax so much that the eggs would just _slide_ right in!

He didn’t get to test that theory exactly, considering that Dib bucked his hips up into Sister’s body and the first egg popped right into place. 

Dib and Sister’s pleasured screams were in perfect unison at that.

“Fuck, oh fuck, Zim, Dib? Holy shit, it’s inside me, look, there’s a fucking bulge in my stomach! Holy shit this is happening, fuck, Dib, do it again, oh my god!”

“Well?” Smirked Zim, when Dib couldn’t force out anything but a stutter. “Give the little lady what she wants. She did ask _so nicely_ after all.”

He nodded feverishly and did his best to try to force the second egg up his cock and into Sister. When he seemed to struggle with it, Zim decided to give the poor alien a hand. He took the hand from off of his sisters breast and used it to give Dib a handjob, trying to coax the egg into his sisters cunt.

Sister had taken to rubbing the egg bulge in her belly. Zim recognized the movement, it was exactly the same way she would rub her clit when she masturbated. He thought back to the days when they were too afraid to touch each other, but unashamed enough to watch each other masturbate.

The only things that had changed about Zim and his sister since then was the size of their dick and tits respectively, and the addition of their new favorite creature. 

Zim took it upon himself to replace her hand with his own, using one to coax his alien lover’s eggs into his sister’s womb, and the other to gently squish the one she’d already taken in. 

Dib moaned out expletives, both in his native tongue and the one he’d learned for his (forgotten) mission. He’d watched two of his own eggs, his spawn, squeeze their way into the living incubator he’d made his mate. A third egg was already making its way down the length of his cock, his body showing no signs of stopping. 

This display absolutely _delighted_ the trio involved.

"Fucking take those alien eggs, you greedy whore." Zim hissed. Dib was taken aback for a moment before remembering the duo's peculiar sexual power dynamic.

"Yes sir!" Sister cried.

"Thank Dib for filling you up and breeding you!" Zim sneered. Dib was vaguely aware of the fact that Zim was humping Sister's ass, if only for the fact that it changed the rhythm at which he fucked her.

"Thank you, Dib!" She whined. Zim delivered a sharp slap to the little space of her flesh that he wasn't grinding on.

"Do it right!"

"Thank you for filling me up and breeding me, Dib!"

Dib just barely bit back an embarrassing noise at that. If not for the vulgarity, for the fact that _both_ of his _alien mates_ were acknowledging out loud that they enjoyed him _breeding_ with them. 

Zim kept the animalistic energy of the room alive with low growls and snarls against his sister’s neck. She looked absolutely delirious, a blissful expression painting her face despite the blush darkening her cheeks and the drool dripping out of her mouth. 

Zim took advantage of this blissed-out trance by grabbing her chin and forcing her to look directly at Dib. 

“Go on then, talk to her. Tell the little whore what you want to do with her, and then _do it_.”

"I-I... I want to fill you with so many eggs that you can hardly move!" He said.

"Fuck, yes! Fill her slutty little womb with eggs! Breed her like a fucking animal!"

Sister was so delirious with pleasure that she couldn't do much of anything besides beg for more. Luckily for her, Dib was more than happy to give her more.

He rocked his hips as hard as he could manage without being afraid he'd break her, and in popped egg three. Sister wailed with pleasure while Zim continued to rub her growing belly, and Dib continued to fuck her.

Eggs four and five seemed stuck together, and the feeling of them moving down Dib’s cock was a more intense pleasure than he’d ever felt in his life. Sister seemed to agree, if her renewed vigor in meeting Dib’s thrusts with her own was anything to go off of. 

She looked up at Zim, who smirked and nodded. The pair stared into each other’s eyes for a second before mumbling out “Twins.” in unison. 

Egg four found itself stuck inside its host, with its companion still stuck inside Dib’s cock. The strange sensation continued until Dib felt a white-hot tear streak down his face, and Zim took pity on his little lovers and jerked him in a way that let egg five join its twin inside Sister. 

Dib didn’t even register that he was talking out loud until he saw his mate’s reactions.

“Fuck, that’s perfect, I’m gonna make you my broodmother!”

"Yes! Fuck I wanna lay your eggs and have your babies!" Sister whined. Zim growled, hips stuttering when she spoke. Even after all this time she could still surprise him with her neediness.

"You'll look so perfect carrying my smeet! You'll be the perfect mother! Im' going to keep you full of eggs for the rest of your life!" Dib moaned. 

The eggs were coming out a bit more rapidly now. Six was nearly halfway inside of Sister, seven was cozy in the middle of Dib's cock, and eight had just barely begun to make itself visible.

One particularly hard thrust and Dib had his cock, and all three of the new eggs, buried inside Sister. Six popped into her womb, and with his hips pressed flush against hers, Dib could feel seven slowly inching out of his cock, the sticky-smooth surface of it connecting with Sister’s inner walls as her body pulled it deeper.

She made an incomprehensible noise when seven slid past her cervix and settled in with the others. 

“Oh fuck, how many of these things are you gonna put inside me?!”

“I-ah! M-maybe ten? Twelve?”

“Oh my god I’m gonna look so pregnant.”

Neither Dib nor Zim was sure they liked what the implications of that statement did to them.

The next _five_ eggs all sort of felt blurred together. By the time the final egg, lucky number fourteen, had started its journey, the entire trio was nearly asleep, exhausted from a long evening of pleasuring each other.

When fourteen joined its siblings in Sister's womb, Dib sighed with a relief he didn't know existed. After nearly six hours of sex and sleep, his cock finally began to deflate enough for him to pull it out of Sister with minimal pain for both parties.

Dib’s tentacle slid back into its sheath, where Zim’s cock hung limp and wet (how many times did he cum just rutting against his sister’s ass?) between his legs. Sister twitched and looked completely out of it, not even responding beyond a nod when Zim demanded to know if she was feeling ok. 

After carrying Sister to the couch, and kissing her forehead when he was absolutely sure she had passed out, Zim sauntered over to Dib. 

Somehow he managed to look intimidating despite the fact that he was naked, and that he and Dib had been balls deep in their girlfriend not 10 minutes before. 

“So, Dib-Thing! How long until she can push those things back out?”

“I don’t...really know? This has never happened before, even back home this was all complete unheard of!”

“Oh, make silence with that sort of talk. You live here, basically with us. _This_ is your home now.”

“O-oh! That’s, um...that’s very...”

“—and as your life-partners and living-mates, we will all do our best to keep each other safe and out of trouble, yes?”

“Of course! But I don’t see what that has to do with—“

“Because she can’t go out in public looking pregnant when you and I are the only ones she ever speaks to.”

"I... I think I understand but, why not? I understand that the illicit nature of yours and Sister's relationship would make you uneasy when it was only the two of you but now that I'm here will people not assume that the smeet are mine?"

"That's only half of the problem, you fool!" Zim groaned and buried his head in his hands. "Humans don't get _that_ big until they're nearly halfway through their pregnancy! You've only been here for three months, and _that_ ," Zim pointed at his sleeping sister's bulging stomach. "That does not occur until... I don't know, five months?! The exact number is irrelevant! She would appear too far along for anyone to even consider the possibility of you being the father."

Dib tried to speak up but Zim quickly cut him off again.

"AND, even if people were to assume that you were the father, she would be mocked relentlessly by our peers!"

“What? Why? If she is old enough to physically carry smeets, why should she not?”

“Oh god, sometimes I forget you’re an alien in the brain too.”

“The what?”

“The...the—the thinking organ? That you use to think? Do you lack one?!”

“My people call them thinkpans.”

“Will you _stop_ calling those dim-witted insects your people? You’re one of _us_ now. _We_ are your people.” Zim growled.

“W-well, yes of course, but I-I...um...”

“Whatever, we’ll worry about it later. For now we need to figure out how long it’ll take her to...return to normal.”

"I'll-I'll take her down to my lab in the morning! We'll run some tests an-and we'll figure out what to do!"

"Yeah, we better." Zim muttered gruffly, sitting down on the floor next to the couch. He reached up to stroke her hair while she slept and Dib felt a singificantly less pleasant knot begin to form in his stomach. It had been so easy to fall asleep with them earlier, when they were so carefree...

He'd be lucky to get even a single minute of rest tonight.

**Notes for the Chapter:**

> Me: Nobody is gonna care about the biological logistics of a xenophillia incest porn fanfic.  
> Also Me: *researches eggs for two hours, learns absolutely nothing*


	7. Uncomfortable Aftermath

**Summary for the Chapter:**

> It’s like she said, they can’t just miss school for a year.

**Notes for the Chapter:**

> Zim, no.

Dib was right. He couldn’t sleep. Zim eventually fell into a fitful sleep, but considering he was sitting up with his hand placed firmly on his sleeping sister’s head and the bags under his eyes were only darkening, it didn’t seem like he’d been truly resting either.

Sister’s stomach hadn’t shown any signs of shrinking or expelling Dib’s eggs, and his computer hadn’t been able to dig up any information on the subject either. For once in his life, Dib was completely in the dark. No past research, no peer-reviewed studies, no lab partners, nothing. 

It wasn’t a test, and it was _terrifying_.

He tried to think positively, if not for himself then for the sake of his mates. But as hard as he tried he couldn't seem to find any silver lining in the situation. 

He spent most of the night reading about human gestation and comparing it to the Irken process, but none of the information he garnered helped. So, instead of going through the proper scientific process to come to a conclusion about how long this would last, he just... guessed.

"Ughhh my body feels like it got crushed in a garbage compact!" Sister groaned, attempting to roll onto her stomach only to be met with immense discomfort. "Jesus, fuck, I figured this would have gone away by now!" 

Zim blinked awake, and his eyes held none of the warmth that they usually did when he woke up to see his lovers.

"When exactly is this gonna, y'know..." Sister gestured to her bulging stomach.

"Well, I'm not sure exactly, but..."

"But what?"

"But I estimate that it will be between three and fifteen months."

The color drained from her face, and Dib recognized the expression from the first time he confronted Zim.

Shock, discomfort, and _fear_.

Dib hated that he was the reason for that expression.

“I mean...I can’t just stop going to school for a year! People would know, they’d talk about it, they’d tell everyone, it would get back to our parents, our cousins...oh god, what are Red and Purple gonna say? What’s _mom_ gonna think?!”

Zim kept his arms wrapped around her upper body, clearly trying to comfort her, but he couldn’t hide the way his body shook, or the stuttering breaths he let out instead of words.

“I-I’m sorry, I never meant for, I mean I didn’t know, and I-“ Muttered Dib, before Sister cut him off.

“No, it’s ok...I mean, it’s not and we need to figure out what the fuck were gonna do, but...I mean, you didn’t know this was gonna happen, we’re not mad.”

Zim, despite his apparent fears, straightened his spine and nodded.

“Indeed. We will need to plan this carefully, but we do not hold you at fault any more than we do each other.”

"So what do we even... what do we even _do_ about this? I mean it's not like I can just go to a doctor, and, y'know." Sister had begun to wring her shirt in her hands. When neither Dib nor Zim could come up with anything helpful she sighed, letting go of the fabric she'd been stretching, and hauling herself off the couch.

"Where are you going?" Dib asked.

"I don't know about you dorks but I need to eat to live. So, I'm gonna do that. Maybe then I'll be able to come up with something that isn't just 'wear baggy clothes and don't act suspicious.'"

Zim promptly moved and stood in front of her, then shoved her by the shoulders back down onto the couch.

“You will do no such thing! We have no idea how this predicament may affect your body! You will stay here and let the Dib do...medical things. Zim will procure the foodstuffs.”

Dib’s antennae perked up. He’d just been assigned a job to do, and it was something he knew well. _Run tests. Isolate any potential issues or complications and enact countermeasures. Help the patient._ Dib could do that. The scientist he was programmed to be was ecstatic, and his instincts agreed. _The alpha mate in his pack trusted him to take care of their hatch-mother. He trusts you to protect her._

Sister sighed and accepted her fate of being condemned to the couch until further notice. 

"So doc, whatcha gonna do in todays appointment?" Sister asked. She gave Dib her usual teasing grin, but it didn't quite reach her eyes. In that moment, his instincts to comfort outweighed his urge to examine.

He took one of her hands between both of his, trying to reassure her in a similar way to how he had seen Zim do it. She seemed to appreciate it, showing her gratitude by lifting his hands up to her lips.

"I'm... I am sure that this is fine." Dib said, sounding much less comforting than he would have hoped. Luckily for him, Sister found at least a small bit of humor in his efforts, as she chuckled softly and let their hands rest together in her lap.

“You’re better at kissing than talking. But really, I’m not too worried. Zim will know what to do, even if it takes a little while for him to make a plan. As long as these things don’t straight up kill me, we’ll all be fine.”

“I...I suppose.”

“They aren’t going to kill me, right?”

“Oh my Tallest, no! I can’t be certain that they’ll be as pleasant coming out as they were going in, but I assure you they will cause you no harm!”

“Yeah, I guess if they hurt the mom your species wouldn’t still be kicking.”

“...we aren’t allowed to do this on Irk.”

“...do what?”

“Procreate, or even take mates at all. It’s outlawed, very illegal, punishable by banishment or death...or worse. Even the spreading of information regarding the process is forbidden.”

“Wait, then how do you-“

“Cloning.”

“Oh.”

“I...I am breaking a lot of rules doing this with you and Zim. If the Tallest or the Control Brains discovered I’d bred, especially with a lesser species...i don’t know what they’d do.”

"Well, _shit._ " Sister said with a nervous laugh. "I guess... I guess we're all kind of fucked if anybody finds out about this."

"I suppose we are."

None of you were looking forward to school on Monday. Coming up with a plan had been hard. Sticking to that plan had proved to be even harder.

The first two classes of the day had been relatively easy. They all shared their first two periods, and no one dared to speak to the trio even when only two of them were present. Once third period had rolled around, Dib, Sister, and Zim parted ways for an hour. 

Without the ability to shield themselves as a group, they were all left defenseless against the prying eyes of their peers.

Sister's third period class was gym. Which is an incredibly unfortunate class to have when you appear to be about four months pregnant. It didn't help that some of the girls in her class were _particularly_ nosey. 

She tried to pretend that she didn't notice the stares, she tried to pretend that she didn't hear the whispers, but no amount of effort could block out all of the beady eyes and hissing voices that surrounded her as she changed into her gym uniform.

She listened in on all the other girls whispers of _incest_ and _that weird new kid._ At least none of them had guessed that aliens were involved.

Meanwhile, Zim was having a much more confrontational experience with his classmates.

It didn’t take much to set Zim off under normal circumstances, so so the moment he heard the whispers of the clique of boys sitting in front of him, he went ballistic.

“You know that freaky kid, Zim, the one who’s banging his sister? Yeah, I heard the new kid got her pregnant. Little weirdo had to do incest to get some, and he _still_ got cucked by the future school shooter!”

Zim barely even knew what was happening until he felt blood on his knuckles and heard the sickening crunch of bone and cartilage breaking. He knew he was gonna get in trouble, both with authority figures and peers, but _fuck_ did it feel good to wipe those smug grins off of those kid’s faces. Even if he’d only hit the one who’d been talking, that kid’s broken nose was sure to send the message.

You don’t fuck with Zim’s family.

Zim smirked at the rest of the clique as the teacher dragged him and his victim by the back of their bloody shirts to the nurse’s office. The shock and fear on their faces made everything worth it.

His sister would undoubtedly be pissed that he immediately resorted to violence, and she'd be even more pissed that he'd gone and gotten himself suspended for fighting. But it still felt like the right thing to do. How else was he supposed to protect his families honor? Communicating with his peers was never his forte, so instead of words he used fists.

Dib was nowhere near as physically inclined as Zim was when it came to confrontation. 

So when he was swarmed by a small group of kids all inquiring about his relationship status in regards to the sibling duo, he was unsure of how to respond.

"So Maia sent a picture of Zim's sister in the locker room and she looks _super_ pregnant and like I'm not saying that we think you're involved but tell us everything, right now." A girl he was unfamiliar with was leaning over his desk, getting _uncomfortably_ close and asking some more than uncomfortable questions.

“I, uh...I don’t know you.” Said Dib. He’d overheard children being told not to talk to strangers, so surely his non-involvement with these people would assuage them!

“Yeah, so? We’re _super_ curious.”

Dammit.

“Really, I don’t know what you’re talking about—!”

“That’s bullshit and you know it. Look, it’s pretty fucking obvious what’s happening. Either all those rumors are true and Zim’s been getting his dick wet on his sister and you’re covering for them because you’re a pervert, or _you_ knocked her up and are trying to keep it quiet.”

“Please, just leave me alone, I’ve got nothing to do with you.”

“Tell us and we’ll leave!”

“Just go away.”

“No.”

This was undoubtedly one of the most nerve wracking experiences Dib had ever lived through. Though he couldnt be sure of the details, he knew that one wrong word could mean dire consequences for him and his lovers. So he had to speak carefully. Very, very carefully. What would Sister say in this situation? 

"I'm not telling you shit." Ah shit, that's not what Sister would say, that's what Zim would say!

"Oh my God, you guys don't even know do you?" The girl said, her eyes brightening at the possibility of drama.

"Don't know what?!" Maybe if Dib just played dumb things would fix themselves.

"Don't know who the father is dumbass!" 

Things did _not_ fix themselves.

Dib was about to either tear these girls apart with his pak legs or just blow a hole in the wall and run away. If he was really human, he probably would have been sweating. If he was a lesser invader, he might have self-destructed to avoid blowing his cover. 

But he couldn’t do that. He had people to care about now. 

Instead, he leaned back and kicked his desk into the stomach of the girl hovering over him, using the group’s surprise as a distraction so he could run to the front of the classroom and demand (politely, of course) that he be let out of class early to use the bathroom. 

He did not wait for the girls to catch up with him, just left the room as quickly as he could and sprinted to the closest boy’s bathroom. The place was filthy as always, and reeked of organic waste, but he was almost certain the girls wouldn’t follow him here.

He could just...wait it out until they went home, and then he could go find Zim and Sister and they would...figure something out.

He spent another three hours hiding out in a bathroom stall before he received a message from Sister.

[are u with Zim? neither of u are at our lunch table and im concerned]

His own absence he could easily explain, he'd simply lost track of time while he was waiting it out. Zim's sudden disappearance was more of a cause for concern. 

[I haven't seen him.]

[well fuck. he's not answering my texts. where are u?]

[Bathroom. A group of humans swarmed me and demanded answers. We may have a problem.]

[fuck. ok new plan wait until lunch is over n then meet me under the bleachers]

[Affirmative. We will plan our next move there.]

[the next move is skipping class and going to ur place cuz there’s no way Zim went back 2 mom n dad’s place without me]

[Understood.]

Dib wasn’t exactly thrilled that he was spending a half hour hiding in a smelly stall, but at least the wig over his antennae blocked some of the smell. 

Sister was exactly where she said she’d be, curled up in a ball under the bleachers in the corner farthest away from the school. She looked just as scared as Dib felt, and when she saw him, she immediately pulled him into a hug. 

Dib took note of the way she was shaking. He wrapped his arms around her ribs and held her close, supporting her weight so she wouldn’t fall if her knees buckled.

She seemed to be holding back her tears. Dib hoped she’d at least be willing to cry when they were home. He knew humans were easily embarrassed by their emotions, but he also knew how unhealthy it was for them to be repressed.

"We should probably head out now." She said, but made no move to separate herself from him. Instead, she lingered there for a while, clinging to Dib and allowing him to do the same. They only separated when they heard other students entering and exiting the nearby school doors.

With the reminder of other people's existence, they headed off, back to Dib's base, in search of their lover.

**Notes for the Chapter:**

> Zim, NO.


	8. Alien Problems

**Summary for the Chapter:**

> Emotions and plot happen, Dib is creepy voyeur, and we play up the incest aspect of Zim and Sis’s relationship.

**Notes for the Chapter:**

> Zim: Alien problems require alien solutions

Zim was exactly where they had anticipated he'd be. He was sitting on the couch at Dib's house when they got there, acting as though he hadn't gone MIA for the latter half of the school day.

Sister could tell as soon as she walked through the door that something was bothering him. She didn't even have to see his face to know it, she could practically feel the tension in him.

"Zim? What are you doing here? Why'd you leave in the middle of the day?"

“I may have made a _tiny_ error.”

“Oh boy. How disastrous, on a scale of deleted-your-Minecraft-save to assassinated-the-Queen-of-England?”

“Firecrackers in Purple’s bowl of Rice Krispies...again.” Zim said with a smirk.

“Oof. Suspension?”

“Indeed.”

“If I may cut in...” interrupted Dib. “What is a suspension?”

“Zim isn’t allowed back at school for a week. It’s a punishment.”

“I thought it was traditional for students to dislike school? Why would forcible ejection be a punishment?”

Both the siblings shrugged.

"It's different when someone tells you you can't go. Plus he get's an F on all the assignments he misses while he's suspended and he doesn't get to make them up later. So his grades are gonna tank and mom is gonna be pissed." Sister plopped down on the couch alongside her brother, stretching her legs out onto the coffee table.

"She'll only be angry if she _finds out_." Zim corrected. He'd gotten into the habit of making fake report cards in middle school, by now it was just second nature to do so even when his grades were good.

"What did you do this time? To get suspended, I mean." Sister asked.

Zim slumped down in his seat, as if he were trying to physically hide from the question. 

"Zim... What did you do?" 

Zim mumbled into the collar of his hoodie, but neither Dib nor Sister could understand what he was saying.

"Zim. What. Did. You. Do."

"Zim _may_ have punched someone in the face for speaking ill of his sister..." He said, refusing to maintain eye contact.

Sister opened and closed her mouth a few times, but no words came out.

“Zim _may_ have broken his nose.”

“Let me get this straight. Someone was spreading rumors about us, the same thing they’ve been doing since we were 7, and you _broke their nose_?”

“Yes, that’s right.”

“I know logically I should be mad, but that’s kinda hot.”

Zim’s sheepish expression was very quickly replaced with a wolfish grin. Dib sat silently on the seat next to him, careful not to disturb the dialogue his loves were carrying out. 

“If I knew you would react like that, perhaps I would have done this sooner!”

“And see, that’s exactly why I didn’t say this earlier.”

“It is too late, dear sister-of-mine. I know everything now, and will not forget anytime soon!”

Despite the... _uncomfortable_ scenarios that had brought them here, Dib found himself smiling at the antics of his mates. Even with everything going wrong, he was happy to be with them.

"Let the record show that this is not me condoning violence! Especially when it gets you suspended!" She insisted. 

"Of course, I believe you. One hundred percent." Zim said, with a self satisfied smirk.

"You liar!" Sister said, nudging his shoulder. For a moment the world felt a lot more gentle and kind than it had earlier. But, as all good things must come to an end, so did their moment of relative peace. 

"Seriously though, we need to figure out what to do about _this_ ," she gestured vaguely to her bulging stomach. "Because if every day is gonna be like today then all three of us are gonna end up getting expelled. God knows nobody will leave us alone now that Punchy McPuncherson over here has gotten in trouble."

“If you give me some time, I’m sure I can...er, ‘science something up’ as you put it a while back.” Interjected Dib.

“Fantastic! Alien things must be solved with other alien things.” Agreed Zim.

“Yes, so you two...do whatever humans do to calm down. I will be in the lab!”

Dib darted off to the basement, mind racing with ideas on how to approach the issue. As he sat down to start working, he turned his lab computer’s screen on, and activated the cameras he had in the living room. It wouldn’t do much good if he couldn’t observe his mates, just in case something happened.

Something did, but it wasn’t what Dib would have expected. Zim pulled Sister into his lap and rested his chin on the top of her head. He looked pensive, and sad.

“You know I love you, yes?”

“Of course, Zim. I’ve never doubted it.”

“And you know I wish you to be happy, yes?”

“Well, yeah? Zim, what are you talking about?”

“I simply...I wonder if you would not be better off... _happier_...with him.”

"Oh, Zim, I don't- I mean, you know I could never..." Her voice wavered, and the tears she'd been holding back earlier had reformed in her eyes.

"It would be much simpler. You would have a more _normal_ relationship."

"More normal relationship? He's an alien!"

"And I'm your _brother_."

"No."

"What do you mean no? You can't just ignore that I’m your brother!"

"No, I meant it as in ‘no, I wouldn't be happier or better off with just Dib.’ I need you, Zim. You're my whole world. I thought you knew that."

“I...I just...you deserve...normal things! Like...picket fences and apple pies and...dogs! Fuck, I don’t know!”

“Ok, first off we already have a dog, Gir basically lives in our backyard. Second off, I fucking love you. I love Dib too, but that doesn’t mean I love _you_ any less. I need you, I’d be lost without you.”

Zim didn’t speak. He snaked his hand up and threaded his fingers in Sister’s hair. She tilted her head to lean on his shoulder and the pair just...sat there. Zim held her close, and she relaxed in his arms. It looked like something Dib wanted to be a part of, but shouldn’t. 

He made a mental note to acquire an apple pie, and whatever a picket fence was.

While Dib worked at finding a solution to the problem of the Eggnancy, the sibling duo upstairs had entwined themselves together. Sister was determined to show Zim just how much she needed him. She turned to straddle him, arms wrapped around his shoulders while she laid slow, gentle kisses on his cheeks, his neck, and finally his mouth. 

It was a far more tender initiation than either of them were accustomed to, but neither of them were complaining.

"I love you, Zim." She whispered into his open mouth, before plunging back in for another kiss. "I love you, _big brother._ " She whispered as she rolled her hips.

Zim flushed red, a color Dib had never seen him turn before. Something about what Sister was saying, either her more aggressive tone or the words themselves, were reducing Zim to a blushing mess _very_ quickly. 

Zim let his hands rest on her hips while she reached impatiently into his pants with one hand and pulled aside her underwear with the other.

Dib knew on some level that he _could_ go up and join them, but...something about this, watching them act organically without him, was making Dib want to stay where he was. 

Maybe if he stuck his own hand under his tunic and touched himself the way he’d seen his male lover do, he’d finally figure out what all the fuss over it was.

Zim seemed content to let her take the lead for once, and the scientist in Dib was immensely curious about the change. But science wasn't exactly his highest priority at the moment. Although, if he had to guess, it probably had something to do with her emphasis on their sibling relationship. Something about the way that she purred when she called him _big brother_ made Zim shiver, and his reaction only served to arouse not only his sister but Dib as well.

"I love you so much. I love you and I'm gonna prove it to you, okay? I'm yours big brother." She whispered, aligning Zim's cock with her entrance. 

Dib's hand wrapped around his tentacle cock. Or, more accurately, his tentacle wrapped itself around his hand. The sensation was nowhere near as pleasant as being inside of Sister (or having Zim inside him). But it was still a damn good feeling.

With everything that had happened, between the sudden first time he’d had with the siblings, his first heat, and the many, many, _many_ times he’d come home and joined in on their sexual escapades, Dib had never really taken the time to explore _himself_. 

Oh well, no time like the present.

Three fingers wrapped around the base of his cock was not nearly as satisfying as five, but Dib didn’t mind. The tentacle had a mind of its own, wriggling and writhing in his grip like it was looking for something. 

Dib squeezed the base, and pulled his fist along the thing’s entire length. He tried to time his pumps to match the slow, gentle pace Sister was setting for Zim. Oh dear sweet stars almighty, the feeling was fucking _electric_.

He couldn't help but whimper and moan along with his lovers, even though they couldn't hear him. 

When Sister buried her hands in Zim's hair and tugged him in for another long kiss, Dib used his free hand to play with his antennae the way that Zim loved to. It made his whole body twitch and his cock leak even more fluid than it already was. 

There was something so inherently erotic about just watching the siblings make love. Dib couldn't quite pin point it but he suspected his own fascination with observing them behaving naturally probably stemmed from the first time he'd watched them. He was so confused then, so unaware of his own arousal. He was _very_ aware now.

Dib had an idea. A wonderful, terrible, amazing idea. If he just held his cock the right way, and pushed it in the right direction... _oh fuck_.

The tip of the tentacle found the entrance to his slit, and wriggled its way in as far as it could go. Hand no longer occupied, Dib was free to grab the ends of both his antennae and rub at them like mad. 

The feeling wasn’t as intense as mating with his...well, _mates_ properly, but fuck if it didn’t feel good. He was sure the chair he was sitting on would be permanently stained blue from the obscene amount of fluid dribbling out of him, and he was sure it would be worth it.

The pleasure was only heightened by the sight of his lovers rutting against each other on the couch, no doubt leaving similar amounts of fluid on the fabric.

Sister broke another long kiss with Zim, tilting her head back and moaning.

"God, you still make me feel like a virgin sometimes. Do you remember how good it was that first time? I saw stars the whole time. I get so horny just thinking about it." Sister said. "Tell me about it, about the first time you fucked your little sister." She pleaded. Zim was more than happy to comply.

“Fuck, I didn’t even mean to at first. I just wanted to cuddle but you kept grinding your ass up against me, you were a desperate little slut even then!”

“Pfft, I was desperate? You’re the one who grabbed my tits and held me down on your dick when I tried to get up for water!”

“You were _absolutely_ desperate, considering you’d soaked your panties before I even touched you! Fuck, I could _smell_ the sex on you, _little sister_.

“Oh, as if you didn’t pop a stiffy and try to look under my skirt whenever I wore dresses.”

“You’ve always been a fucking tease. Even when we were in front of our cousins, you couldn’t help yourself, could you? You just _had_ to reach under the table and touch me.”

"You know you loved it!"

"Yeah almost as much as you loved me bending you over the couch after everyone else had gone to bed." 

"Fuck, yes that was _good_. That was the first time you spanked me."

"And you came so hard it made you cry." Zim's hips were twitching erratically, he was losing the steady pace that Sister had set for him, and Dib was struggling to keep up with their movements.

"It was _so hot_. You hit me and it felt good because—fuck! It felt good because you _love_ me!" Sister whined. "Give me all of your love, big brother!"

Zim growled out a breathy “fuck” and bit into Sister’s shoulder. She screamed out Zim’s name and snapped her hips into him a final time before shivering and going limp in her brother’s hold.

Zim bucked up and managed two more shallow thrusts before he lost himself to his own orgasm. Dib pressed his thighs together and tugged on his antennae one more time, harsher than before, and spilled his seed onto the already ruined chair. 

Zim pulled her hair to one side and pressed a gentle kiss to the other side of her neck. Then another. Then another, and another, and he kept going until Sister erupted into a giggle fit and slid off of him. 

“I take it you’re feeling better?” Asked Sister, once her laughter died down.

"Zim is feeling significantly better." He said, relaxing back into the couch. Sister kissed his nose and sidled up next to him. 

"Good. I'm glad." The duo sat and basked in the afterglow for a few minutes before Sister spoke up again. "I wonder if Dib's found anything useful."

Shit! 

He should probably start doing some actual work, or research, or really do anything more productive than masturbating.

Well, it’s not like he hadn’t had the idea before, just in a different circumstance. Dib wasn’t sure it would be the easiest method, but it was sure to at least work. After cleaning himself up and redressing, Dib found himself in front of his very blissed out mates. 

“So, Dib-Thing! Any ideas on how to solve this predicament?”

“Well, um...yes! But I do not know if...uh...just, don’t panic when I suggest it, ok?”

Zim and Sister gave him a suspicious look, but nodded.

“I’m going to try and speed up the incubation process, and then you’re going to lay them.”

**Notes for the Chapter:**

> Yeah the egg laying chapter is inevitable. Prepare yaselves.


	9. Bathtub Birthday

**Summary for the Chapter:**

> They’re almost as fun coming out as they were going in!

**Notes for the Chapter:**

> It took all of my self control to not fill this chapter to the brim with egg puns.

"And you're _sure_ that this will work?" Zim inquired, watching his sister shed her clothes.

"I am at least 65% sure that this will work." Dib responded, too distracted by the chemicals he was mixing to be enticed by his lovers body.

"Gotta say, I don't really like those odds!" Sister chimed, kicking her pants off. Dib slid his chair back, away from the desk.

"Well, it's the best option we have. Drink this." He said, handing over a thin test tube half full of a deep purple liquid. Without hesitation, Sister tossed back the drink, only to gag and cough after swallowing it.

"God that tasted like ass!" She whined, wiping at her mouth. "So how long do I have to wait before it- _oh_." Before she could finish her sentence, her water had broken, spilling onto the floor.

Dib’s antennae shot straight up, his alertness palpable in his posture and expression. He quickly ushered Sister to the closest bathroom, with Zim following suit. She gingerly laid down in the bathtub and the boys knelt beside it.

Zim turned on the faucet, grumbling out an apology and adjusted the temperature when Sister hissed and shrunk away. Dib actively avoided getting splashed by the water, while Zim didn’t seem to care. Zim was wearing a tank top and a ratty pair of sweatpants, and Dib thought for a second that he probably should have done something similar.

“S-so!” Said Sister. “Uh, how will we know if they’re...y’know... _alive_?”

Dib adjusted his goggles and put on a composed facade so she wouldn’t worry. 

“W-well! If they’re viable, they’ll be hard and colorful, and slightly bioluminescent. If they’re not, they’ll be squishy and gray.”

“And how...how big do you think they’ll be?”

“Approximately the size of...perhaps your fist?”

Sister paled.

"I'm gonna get torn to shreds!" She wailed.

"Only if they're viable! If not, they'll be so soft it'll be nearly as easy as it was to take them in!" Dib explained, in a feeble attempt at comforting his lover.

"Uh, yeah that wasn't exactly a cake walk either!" She replied. With a sharp gasp and a buck of her hips, she realized one of the eggs was attempting to make its way out.

Dib instinctively laid his hand on Sister’s swollen belly, gently pushing and rubbing circles on it to help the eggs move faster. 

Sister snatched Zim’s hand away from the faucet handles and held it up to her chest. In an attempt to calm the tense nature of the situation, or distract Sister from her current predicament, Zim squeezed her chest. She made a noise somewhere between a squeak and a moan.

“Was that a ‘that’s super sexy and hot please keep doing it’ noise, or an ‘ouch that hurt a lot please stop’ noise?”

Sister made no move to respond, just repeated the noise again when Dib’s hand reached a bit lower.

Two of his three fingers gently slid inside of her and moved around, fishing around for the obtrusive objects.

“What the hell are you doing?” Asked Zim.

“I-I thought, maybe I can just...pull them out, one by one? It might help too...speed up this process.”

“Ah, so the tentacle you’ve got wiggling around down there has no ulterior motives then?”

"N-no! Of course not, I just-"

"Stop talking." Sister commanded, both Dib and Zim immediately silencing thenselves. "Keep... fuck, keep going." She said, grabbing Dib's wrist and pushing his fingers deeper into her cunt.

While she grinded down on Dib's fingers, Zim had taken it upon himself to do his boyfriend a favor by shoving his hand down his pants to play with his tentacle like cock.

Dib gasped twice in rapid succession. First, when Zim's hands touched the slimy skin of his cock, and second when he realized he could feel an egg pushing against his lovers cervix.

When Dib began to gently coax the egg lower, she screamed. It was had to tell whether it was pain or pleasure making her scream, but either way she wasn't twlling Dib to stop.

So he continued.

He rubbed and massaged as Sis pushed, and groaned, and pushed, and fucked herself on Dib's fingers, until _finally_ she had opened up enough to begin forcing the egg out.

Dib slipped his third finger into her, grabbing onto the egg with his claws and gently easing it out as Sister pushed. When it finally popped out of her soaked hole, Dib saw that it was gray and simply dropped it on the tub floor. He forced the sharp tips of his fingers back into Sister’s body, and upon catching an eyeful of another of his eggs squeezing its way out of her, bucked his hips up into Zim’s hand.

“H-how many were there, again?”

“Fourteen?”

“Fuck.”

Sister took a deep breath and let it out with a shudder, then inched herself slowly down the tub until the small stream of warm water from faucet was hitting her thigh.

Dib moved her a little higher up, to avoid his hand getting wet, and felt around inside her again for the egg he’d seen. His claws met the squishy surface of the thing, and Sister let out another whine and a tear Dib hadn’t noticed forming.

He didn't even notice the way his antennas wound themselves in her hair. He was too caught off gaurd by the chirping noises he was unwillingly emitting. 

Surprisingly, the chirps seemed to soothe Sister. Not a lot, but enough that her body had relaxed enough to suck the 2nd egg back in. 

She cried out and rutted against Dib's hand at the feeling of the egg sliding back into her. 

"It won't come out!" She howled.

"Just keep pushing, you'll be fine." Instructed Zim, sounding awfully calm for someone who was watching his sister give birth to a bunch of gelatinous eggs.

She nodded and followed his instructions, trying to force the egg back out to where Dib could grab it. He tried to help it out by scissoring open his fingers and trying to let gravity do the work.

Instead what happened was Sister nearly screamed, and the second and third egg dropped fast and hard enough to push Dib’s hand out of the way. Two more slimy gray spheres rolled onto the bathtub floor, and Dib could feel an equally slimy texture on his own nether regions.

Zim on the other hand was very clearly biting back a laugh, much to his sister’s chagrin.

“What’s so funny?”

“Oh, nothing. Just that our little alien over here creamed himself over those stupid eggs already.”

"Dib, did you actually...? Oh my god." Sister groaned. Peeking over the rim of the tub, she saw Zim's hands still hard at work inbetween Dib's legs. "No shit dude, you're the one who's been jerking him off this whole time!" She chided.

Dib's brain had gone a tad bit numb from the pleasure, and instead of focusing on something silly like a conversation, he instead focused on the more pressing matter: his eggs.

Dib carefully slipped the very tips of his fingers past Sisters cervix, spreading it open to help usher the eggs out. Of course, she screamed at the sudden intrusion, and her scream petered out into a broken moan as Dib plucked one of the eggs and pulled it out of her. 

Maybe it was something about the speed at which the egg was dragged out, or perhaps it was something to do with the feeling of Dib having control over such an intimate part of her body, but something about that new egg being pulled out of her wracked her with an orgasm- the kind that you feel throughout your entire body.

Dib, even through his instinctive lust and his body _screaming_ at him to find someone or something to put his dick in, still tried to be soothing when he rubbed Sister’s belly with the hand that wasn’t inside her. 

Zim didn’t bother letting go of Dib’s still-dripping cock, just letting Dib fuck himself silly on Zim’s hand. He kept his attention on his sister, mumbling simple praises and encouragement into her ear.

Dib and Sister were both enjoying the sensation of Dib’s fingers trying to attach themselves to another egg, but when he finally grabbed one and tugged, Sister sobbed at the overstimulation. 

The egg Dib has grabbed was attached to another egg, still stuck in her womb. A second gush of water pushed out past Sister’s pussy lips with the conjoined eggs, finally prompting Dib to take off his gloves.

He once again slid his fingers inside his mate, and a wave of renewed heat surged through him, and the way his dick thrashed was not going unnoticed by boy holding it.

“What’s that about?”

“O-oh my Stars, she’s so warm...!”

"Yeah, I bet she is." Zim teased, pressing Dib against the edge of the tub, trapping him between the bath and himself. "I can't believe you're horny right now. I mean look at her, the poor girl's absolutely miserable!" 

Sister was in no way miserable. Overwhelmed and uncomfortable certainly, but the pleasure of being fingered in between pushing eggs the size of her fist out of her was much more intense than any discomfort she was experiencing.

"You want to fuck her, don't you?" Zim whispered. "You wanna slip your dick in and poke those eggs around with your cock." Dib could have cried, the feeling of Zim's hand on his cock, as well as the feeling of Zim grinding against him, combined with the filthy things he was saying, made his entire body shudder with pleasure. If he weren't already sitting down he was certain his knees would have given out.

Zim pulled Dib’s already soaked black pants down, letting the alien’s bright blue cum drip on the floor as his cock thrashed in Zim’s loose grip. Sister whimpered at the sight, bringing her hands up to her face to hide her blush, and weakly pushed the next egg into Dib’s hand. 

“Th-that’s six! You’re almost... _oh my stars please don’t stop_ , you’re almost ha-halfway done!”

Sister just whimpered again, though she didn’t seem particularly upset at the notion.

“Silly, stupid, little alien.” Teased Zim, with no real malice behind his words. “Look at the poor girl, she’s all swollen and sweaty because of you, and here you are fucking yourself on my hand to the thought of doing it again.”

Dib shied away from Zim’s stare, but made no move to deny the accusation.

“She hasn’t even finished pushing the product of your _last_ little escapade out!”

Sister pulled Dib's hand up by the wrist, dragging his fingers out of her cunt and pushing them into position to rub her clit. Normally when she did something like that, some sort of change in position, she would look Dib in the eyes, as if she were telling him to prepare himself for more, but she didn't.

This time, she was too focused on the blue, gooey fluid that had been gushing out of her in between eggs. 

When Dib didn't immediately respond to her relocation of his hand, she responded for him by rubbing his fingers in messy circles around her clit.

"Fuck's sake, _both of you_ are horny? I can't believe you two. Such needy little whores, both of you." Zim chided, unbuttoning his pants and shimmying them down to his knees.

Zim positioned himself behind Dib, biting his lip and hissing as he slid himself into Dib’s body. One hand stayed wrapped around Dib’s cock, while the other snaked up to his head and tilted it to the side, giving Zim better access to his neck.

“Clearly, you two can’t satisfy yourselves enough. So how about I take care of our horny alien pervert, and he can make sure that our sweet little sister is having fun, hmm?”

Dib nodded feverishly, trying to keep his hand from shaking too much as he refocused on Sister and the slick fluids leaking out of her. 

Sister opened her eyes for a moment, just long enough to see Zim snap his hips up into Dib’s fluttering hole, and to watch Dib bite his lip and fail to keep a string of drool from falling out of his mouth.

It was difficult to tell whether her moan or Dib's was louder.

Not that it really mattered. Between the sound of running water, whining, and slick holes being pushed to their absolute limits, it was a miracle any of them could even differentiate the sounds.

Sister managed to push out another three eggs, all in rapid succession, after her second orgasm. In fact, it was those three eggs being pushed out of her that gave her her third orgasm. Watching his lover experiencing such intense pleasure made Dib cum too, his slick hole gripping Zim's cock like a lifeline.

"You can do it sis, just a couple more!" Zim groaned, grinding his hips into Dib's ass.

Dib whined and pushed his hips up to the side of the tub, letting his tentacle squirm over the edge and drip into the puddle of slick that was forming near the the drain. Sister reached over and took the thing in her hand, squeezing and pulling the gelatinous flesh. 

Dib returned the favor by slipping his hand into her folds again, coaxing the remaining few eggs out further. Without his gloves, Dib could feel the slick inside Sister, a pale blue mix of her own lubricant and the fluids he’d forced inside her. 

Dib was so caught up in his thoughts, he almost didn’t feel the egg he’d pulled out puncture under his claws. Whatever, it was gray anyway. Dib was _much_ more focused on the feeling of Zim’s thrusts getting sloppier.

Sister's orgasm and subsequent gush of fluid and eggs was merely a passing thought to Dib when she leaned over to allow his cock into her mouth. The feeling of her hot warm tongue touching his oversensitive dripping cock combined with the feeling of Zim bucking into him with reckless abandon was enough to make Dib cum so hard he doubled over.

Not that it stopped Zim, or Sis from continuing what they were doing. Well, actually Sis didn't appear to be doing very much, she was mostly limp, her body finally relaxing from the tenseness of giving birth. Her mouth hardly moved, even with Dib's cock exploring every crevice of it.

Zim was perhaps the only person still actively moving, but even that didn't last long. He came in Dib with a growl and a bite to Dib's neck, leaving both his teeth and his cock buried in his alien lover.

Zim bucked up twice with weak thrusts, riding out his orgasm. When he finally slipped out and let go of Dib’s head, the alien dropped onto his hands and knees like a folding chair. Sister reached over and weakly patted his head, but continued laying still in the tub. Zim fell back onto his butt and sighed contentedly, running his clean hand through his sweaty hair. 

“So...everyone ok?”

Dib nodded softly, while Sister managed a lazy thumbs-up. 

“Well good. I’m going to get us all some water, so just stay there and try not to keel over while I’m gone.”

Dib and Sister sat in exhausted silence while they waited for their lover to return, but snapped to attention as best they could when he came back with his phone in his hand and the color drained from his face.

“We may have a slight problem.”

“Shit.” Said Sister. “What happened?”

“Mom just texted me. Aunt Miyuki is coming over.”

**Notes for the Chapter:**

> So many dud eggs. Well at least breakfast is sorted.


	10. Human Problems

**Summary for the Chapter:**

> Family dinner, but of course nothing can ever go right for these three.

**Notes for the Chapter:**

> So nobody’s confused-
> 
> Corrine and Brian: The Control Brains, Zim and Sister’s parents.
> 
> Miyuki: Corrine’s Sister, Red and Purple’s Mom.
> 
> Spork: Miyuki’s husband, Red and Purple’s father.

Giving birth to a bunch of eggs in a bath tub was undeniably stressful for the strange little polycule, but somehow they had found an even more stressful experience to endure. A family dinner with Zim and his sister's parents, aunt, and worst of all, their cousins.

When their mother told them that their family was visiting, Zim and his sister processed the news like they always did.

Step one: dread.

Step two: frantically attempt to conceive some sort of a defense plan against their cousins.

Step three: get too wired trying to plan, and have sex to alleviate the anxiety. 

Step four: come up with an actual plan or resign to being teased mercilessly at the hands of their cousins.

The problem with making plans was that no matter how many countermeasures the pair of them took, Red and Purple always somehow managed to derail everything. If Zim arranged for his aunt and mother to take the twins to a movie, they’d conveniently get sick and have to stay home while Miyuki and Corrine went to the movie by themselves. 

After the... _incident_ a few Christmases ago, Red and Purple had apparently made it their life’s work to torment their cousins as much as possible. Somehow that meant that whenever there was a chance for them to be alone, Red would orchestrate the scenario and take full advantage of a lack of prying eyes.

It’s not like Corrine really cared about her children, and her husband was even more distant, if that were even possible. Zim couldn’t ask their aunt for help either, as Miyuki was too busy gushing over her perfect straight A student twins to bother noticing that they’d cheated their way through their academic careers. Spork was...well, Spork only cared about whatever Miyuki cared about. 

All that meant Zim and his sister were left to fend for themselves against their “family”, with no friends or guardians to help shoulder the burden. 

Until Dib.

It was Zim's idea to bring Dib into the mix, initially saying that they should just go over to his place and hide there until their families leave. That idea was quickly shot down due to the fact that Corinne would _never_ let them out of the house while her sister was over. The siblings had long suspected that their mother and her sister always seemed to have some sort of competition going for who could raise the better children.

Not that either of them were really winning.

So whenever aunt Miyuki and uncle Spork and the twins came to visit, Zim and his sister had to be there, so that they could host and show off their lovely little family. Even though they spent so little time at home that they'd nearly forgotten where they keep the silverware.

So instead of going to Dib, Dib came to them.

In a slightly more normal household, a teenage girl bringing her boyfriend over for a sleepover at a family gathering would be unacceptable. But considering the uncomfortable rumors circulating the siblings paired with the amount of times Corrine had told them off for being just a little too close, Zim could tell she was happy that Sister had managed to snag herself a “normal” boy.

To Corrine, it meant she’d been social and made a friend. It meant she was feeling normal teenage girl things. It meant she was becoming less like herself.

Just like her mother wanted. 

When Dib showed up on their doorstep in a button up shirt and slacks, he was welcomed with open arms. At least, as open as they could be considering who they were attached to. 

So Dib found himself being ushered by a very old fashioned and proper-looking woman to a large dining table that seated another, more professionally dressed woman, Dib’s alien lovers, and (presumably) the pair of twins they’d been so spun up about. 

At first, Dib didn’t understand the fuss over the twins. Even with their malicious, wolffish grins and grating laughter, their color coordinated hoodies and sneakers didn’t exactly scream “danger” to Dib.

The businesswoman on the other hand, _terrified_ Dib. Everything about her was immaculate and pointed, from her navy blue eyeliner to her heels, sharp enough to stab someone. She carried an aura of control, and her piercing gaze reminded Dib of the glares and snide remarks that much higher ranking elites would give him. 

Her voice did nothing to change Dib’s opinion of her. Cold and judgmental in a way that sent chills up his spine.

“Is this that little man you were prattling off about earlier, Zim?”

“Yes ma’am.”

Not once that night would she speak directly to Dib, instead deferring to Zim and Sister, sometimes even their mother when asking about him. Sitting right next to her at the dinner table was a VERY uncomfortable experience, like she was watching his every move despite her eyes pointing anywhere but him. 

When Corinne entered the dining room and began to fill the table with serving dishes (the fancy crystal kind, that Sister said she only ever brought out when aunt Miyuki was over) the twins acknowledged him for the first time.

"So is this kid like, a foreign exchange student or just like, really poor, or what?" Purple asked.

"He's my boyfriend." Sister replied, with a well practiced, ever so slightly too sweet tone- one that Dib was not at all used to.

Dib forced a smile onto his face, quietly confirmed their relationship, and braced himself for the fallout. 

Fallout he certainly got. The twins shot each other a look, all narrowed eyes and tight smiles. Dib found himself wondering if he’d underestimated them. The one in red spoke first, followed by his cool-toned counterpart.

“So, where’d you meet the little stutterbug, a bathroom stall or a street corner? Did you have to fight Zim for her?”

“Hah, yeah! And we wanna know how you have conversations with them, can you even hear yourself over Zim’s screeching?”

Zim and his sister both flushed pink, enough that Dib noticed but apparently not enough for the rest of the family to care. 

“H-he...we met in—in the li-library. We have a s-s-study period...together.”

Dib was confused. He’d never heard Sister speak so imprecisely before, she was always so sure of her words before, why was she struggling with such a simple skill now? He chalked it up to a fear response and decided to look into it later. For now he had his companion’s reputations to salvage!

“We share an interest in books, she’s been, er, giving me recommendations.”

“Oh, that.” Spat Red. “Let me guess, Flowers In The Attic? Or something equally fucked up.”

Poor Sister’s blush deepened, and she looked down at her plate like she was holding back tears.

Zim was also being uncharacteristically quiet, but Dib had expected that. The siblings had given him a briefing on the Family Dinner Rules And Regulations earlier in the day.

One rule was that Zim may not under any circumstances, try to argue in his sisters defense and vice versa, because denial only makes the teasing worse.

Dib recalled Sister mentioning that book, back on their first "date," if you could really call it that. He'd read it, of course, and instantly made the connection between the the main character and her brother’s romance, and the relationship Zim and his sister had. 

Knowing the dirty details of the book, it would be ill advised of him to confirm that, yes, they had bonded over that particular story—although, probably not in the way that Red was imagining. So he thought perhaps, if he played dumb maybe he could turn the tables and make _them_ uncomfortable.

"What's that about?" Dib asked.

The twins’ side eyeing only got worse at that comment. Apparently Dib’s plan backfired, considering the giddy but teasing tone the purple twin used.

“Oh, it’s one of her _favorites_. It’s supposed to be a horror story, but she just likes the main character’s love interest. She wants a boyfriend _just like him_.”

The double meaning was not lost on Dib, but luckily for him, the less terrifying of the adults at the table spoke up.

“Oh, I remember that old book. My daughter has always been an active reader, she’s always absorbed in those silly stories of hers. She’s such a gifted child isn’t she?”

“ _My_ sons are both in AP English classes.” Replied Miyuki, smirking at her sister with icy blue eyes, and an even colder tone. “They’re also in extracurricular clubs, which is just _so important_ if you want to get into a good college.”

"Well, of course they are! But you know, they really do have to learn how to form amd manage good relationships when they're young." Corinne bit back. "After all, _so much_ of business these days is less about where you went to school and more about who you know. She's learning the most valuable skill of them all: networking."

Dib could practically feel how much both of his lovers wanted to roll their eyes.

"Of course but you're not going to make it anywhere if you're networking at some community college instead of an ivy league. Speaking of which, Red and Purple will both be applying for each of the ivy leagues. Our goal is for them to be accepted into all of them, and then they can just choose which school to attend!"

Corinne gave her a tight smile and responded with a sharp, "isn't that nice." 

On Dib's other side, he could see Zim visibly growing more and more tense. He recalled that earlier in the week Zim had been incredibly upset by an argument with his mother about post secondary school options, and this battle between his mother and his aunt certainly didn't ease that stress.

“Even still, sometimes you don’t need a proper Ivy League degree to succeed. If I recall correctly, doesn’t your husband have a GED?”

“Hmm, well I suppose it works for some people.” Miyuki shot back, unbothered and uninterested. “If your daughter gets a little prettier, and is willing to settle for being a _trophy wife_. Speaking of that, where’s Brian? I’d have loved to give him my regards.”

“ _My_ husband is working late. He’s in a very important position, in fact his company is thinking of promoting him to executive regional manager.”

“Oh yes, I remember those sorts of promotions. Getting started in a job can be such a rush, can’t it?”

“Hey, mom?” Red butted in. “We’re all done, and it looks like our little cousins are too.” 

Miyuki immediately stopped her tense interaction with her sister, turning all her attention to her sons.

“Yes, my darling? Do get to the point, it’s unbecoming of a respectable young man to dawdle.”

“I was just wondering if we could all head upstairs to hang out, so you and aunt Cora can catch up.”

Dib didn’t enjoy the smirks the twins were biting back.

"Of course! I mean, as long as it's okay with you," Miyuki's side eye could have killed a lesser woman, but Corinne clearly didn't intend to back down, staring her sister down across the table as she spoke.

"Of course. You kids go have fun. I think I'll break out a bottle of wine. I've been saving a special one for your next visit." 

The twins immediately stood up, Zim and his sister reluctantly following suit.

Dib stood up and leaned his hand towards Sister, who grabbed it immediately. Zim reached out to them for a moment, but very quickly decided against it and pinned his hands to his sides.

Despite not owning nor dwelling in the house they were in, Red and Purple were more than comfortable leading the group to Zim’s bedroom. In fact, they seemed like they were more aquatinted with the house’s layout than the pair of siblings that technically lived there. They also seemed like they were planning something, all calculated movements and hushed whispers interspersed with snickering.

“Hey, Pipsqueak, you still got the Sims?” Asked Purple, cutting the silence.

“Uh, yeah.”

“Good! I’m gonna trap them all the pool like last time.”

“Two times ago.” Said Red.

“What?”

“You trapped them in the pool two times ago, last time we were here you just made all the sims in individual tiny rooms with no doors or toilets.”

“Oh yeah! Hah, that was good.”

Sister sighed, at least this time she'd had the sense to prepare an unplayed save for her cousin to destroy.

She'd been tempted to add a couple of broken mods to the game, or maybe even ask Zim and Dib to program her something that'll fuck with Purple while he played. But she knew a little too well that Purple was easily frustrated and prone to breaking her shit, so she resorted to just loading a new file and praying that he was dumb enough to click the first one he saw.

As soon as her cousins crossed the threshold into Zim's bedroom, she had a terrifying thought. _Did she remember to get her panties back from Zim's room the other day?_

If she didn’t, maybe at least she’d be able to distract her cousins with games long enough to stuff them somewhere they wouldn’t notice. 

Sister was so distracted by the thought, that she didn’t notice Purple sneaking up to her until he lifted her shirt a couple inches and pinched her side.

“Gotcha!”

Sister made an embarrassed noise and pulled her shirt back down, blushing darker when her cousins laughed out loud at her reaction. 

“Oh come on, it’s not a big deal. It’s nothing we haven’t seen before, _right_?” Grumbled Red through his teasing snickers. “Besides, I’ll bet you let this kid do way worse shit to you when nobody’s looking. In fact I’ll bet that—“

Red had taken to pinching and poking Sister through her shirt, mimicking what his twin had been doing moments earlier. For some reason, when he pressed right in the middle of her stomach, he stopped entirely.

“Whoa. Hey Pur, get over here and feel this.”

“Ew, gross. I’m not _Zim_ , I don’t want to _touch_ her.”

“No, no, trust me, this is fuckin weird.”

"Eugh, okay fine." Purple poked her, just below the belly button. "What the fuck?"

"I know right? Why's her stomach feel so... I dunno, hard? _Clearly_ it's not because she's been working out, I mean we can all tell that she's been getting kinda fat."

Zim realized it before either of the twins did, and for a brief moment before they caught on, he locked eyes with Dib, seeing that they'd both put the pieces together at the same time. 

Sis was too busy being prodded, fruitlessly batting her cousins hands away, to come to the same realization that there was a very slight, totally not at all likely, absolutely infinitesimal chance that she'd missed an egg.

Red caught up to the narrative next, a dangerous smile creeping over his face as he did.

“Wait...hold on, Pur, do you think...?”

“What?”

“That she’s...y’know...!” Red glanced at Zim, then Dib, then back at his twin, who put the pieces together pretty quickly after that.

“Holy shit, if she is, she’s gonna have to worry a lot more about _this_.” He said, grabbing another handful of her stomach.

Red turned his attention back to Sister, tossing an arm over her shoulder and gripping a little too hard. To the outside eye it may have almost seemed sweet, but really it was just uncomfortable.

“So, was it the creepy trench coat kid who knocked you up? Or do _old habits_ die a little to hard?”

She couldn't help but glance between Zim and Dib, silently pleading for either of them to nip this conversation in the bud before it could grow any more. Unfortunately, her frantic gaze was very misunderstood by her cousins.

"Oh my god. You don't even _know_ do you?" Red asked with deceptively childish curiosity.

"Young lady does your mother know that you might be knocked up with your own nephew right now?" Purple mocked, and poked her stomach again, but this time she didn't try to bat it away like she was swatting a bug. She hit him. Hard. Or at least as hard as she could with her elbows nearly locked to her sides.

For a moment, the room was still. It was completely silent save for the ragged sound of Sister's breathing. For the first time, it appeared as though she had managed to silence her cousins.

Any pride the trio may have felt over that quickly dissipated when Purple burst out laughing.

“Is that it? I thought at least you’d be able to make it hurt if you _tried_!”

Red picked up on Purple’s energy and laughed with him, even manhandling Sister around a bit and flicking her in between the eyes a few times. Once his laughter died down, he _finally_ turned his attention away from Sister...but turned it towards Dib instead.

“I mean if she didn’t know, that’s one thing, but you’ve gotta be a whole other kind of freak to let her keep that shit up with her _brother_.”

“I...I don’t know what you’re talking about.”

“Ugh, fine, all this bullshit is getting us nowhere. Ok, I’m gonna assume you’re just stupider than you look, and I’m gonna spell it out for you. _She_.” He said, jabbing his thumb in Sister’s direction. “Has been fooling around with _him_ , her _brother_ , since they were at least 13. I know, because I caught them doing it. Now she’s knocked up, and she doesn’t know if it’s yours or his, which means they’ve graduated from kissing to straight up fucking each other.”

“I...um...”

“So how does it feel? Knowing that your girl is a little freak that’s been taking her big brother’s dick behind your back?”

Dib had assumed that this would be an _easy_ mission. His only objective was to be around his humans and (he had assumed) maybe defend their honor when either one of them got called short. But now he understood why Zim and Sister had been so insistent on preparing Dib for this event. 

Not only was this entirely out of his wheelhouse, this was fucking scary! 

He struggled to calculate the proper response to Red's question, but fortunately (or perhaps very unfortunately) Sister spoke up before Red could neg him again.

"You guys are assholes!" Her voice was watery, and it was obvious from her trembling and sniffling that she was about to cry.

Purple immediately started whining in a mocking tone, mimicking her words and fake-crying in the most annoying way possible. Red laughed, and barked out something about her being a crybaby through fits of giggles. Purple spoke up through their hysterics, addressing his twin directly.

“She really is a crybaby! She’s almost as bad as you were when you were her age!”

“Oh shut the fuck up Pur, I wasn’t anywhere close to _this_.”

“Oh yeah? I can remember plenty of time you had to use my hoodie to wipe the snot off your nose after a tantrum.”

“Bullshit!”

“Oh yeah? How about that test you failed in 7th grade? Or that girl who called your dick small in freshman year? What about the half million shitty movies you’ve sobbed over? Or how about when we were 14 and you just couldn’t handle it when— _whoops_.”

“Wait.” Piped up Zim. “When _what_?”

"When, _nothing!_ It's none of your business dork!" Red said, trying and miserably failing at acting innocent. He couldn't even make eye contact with Zim.

"Oh my God." Sister said. In spite of her bewilderment, and the fresh tears that had just slid down her face, she was enthralled at the idea of finally, _finally_ having something to hold over her cousins heads. Especially something as juicy as this.

"No wonder you guys have been so obsessed with us," she said. "You guys have been-" Purple cut her off by slapping a hand over her mouth.

"We did not!" He hissed.

"Oh yeah, well then finish that sentence. Why don't you tell us exactly what it was that he couldn't handle?" Zim said. The trio had finally found their footing and were now _more_ than willing to turn their cousins bullying back onto them.

Neither of the older boys spoke, opting to just glance at each other in panic and shock.

Dib was incredibly proud of what happened next. He watched in awe as the fight crept back into Sister’s eyes, as she bit down _hard_ on her cousin’s hand, and as she laughed and shouted at the room.

“He couldn’t handle Purple’s DICK!”

“SHUT THE FUCK UP YOU LITTLE SHIT!” Screamed one of the twins, not that it mattered to the trio which one it was.

That screaming meant that finally, fucking _finally_ , Zim and his lovers had the advantage.

The advantage, and the element of surprise.

Zim had never felt more vengeful satisfaction than he did at the fear in his older cousins‘ eyes when he finally stepped in front of his sister to face them.

"You know, you can't hold this over our heads anymore." Zim said. "If you expose us, then we expose you."

"In fact, I think we might even have a little something else to tack onto that expose. After all, kids just do what they observe others doing, so how were little Zim and I supposed to know that it's wrong to do incest when our big cousins who we _love and trust, so much_ are showing us that it's perfectly fine?" Sister said, the thinly veiled threat sent a shiver down both of the twins spines.

"Okay, okay, okay, _fine._ we're gonna keep your shit a secret. But we all know that as soon as that little shit," Red pointed at Sister's stomach, "starts to show, you three are FUCKED. And no way is anybody gonna listen to some slutty teen mom, especially when _our_ records are spotless."

“Yeah, yeah, just get out of here. And don’t steal my chips this time, don’t think we didn’t know it was you.”

Red and Purple stalked off with their tails between their legs, Red angrily whispering to a very defensive and annoyed Purple.

The moment they were out of earshot, Zim closed the door and let the giddy grin on his face show.

“Holy fuck. I can’t believe that worked.”

**Notes for the Chapter:**

> Fun fact that conversation between Corrine and Miyuki is based off of one I overheard as a kid between some of my extended family.


End file.
